A Randomized Trial of Inspiratory Training in Children and Adolescents With Obesity

Introduction: Children with obesity suffer excess dyspnea that contributes to sedentariness. Developing innovative strategies to increase exercise tolerance and participation in children with obesity is a high priority. Because inspiratory training (IT) has reduced dyspnea, we sought to assess IT in children with obesity. Methods: We conducted a 6-week randomized IT trial involving 8- to 17-year-olds with obesity. Participants were randomized 1:1 to either high [75% of maximal inspiratory pressure (MIP)] or low resistance control (15% of MIP) three times weekly. Assessments included adherence, patient satisfaction, and changes in inspiratory strength and endurance, dyspnea scores and total activity level. Results: Among 27 randomized, 24 (89%) completed the intervention. Total session adherence was 72% which did not differ between treatment groups. IT was safe, and more than 90% felt IT benefitted breathing and general health. IT led to a mean improvement (95% CI) in inspiratory strength measured by MIP of 10.0 cm H2O (-3.5, 23.6; paired t-test, p = 0.139) and inspiratory endurance of 8.9 (1.0, 16.8; paired t-test, p = 0.028); however, there was no significant difference between high- and low-treatment groups. IT led to significant reductions in dyspnea with daily activity (p < 0.001) and in prospectively reported dyspnea during exercise (p = 0.024). Among the high- versus low-treatment group, we noted a trend for reduced dyspnea with daily activity (p = 0.071) and increased daily steps (865 vs. -51, p = 0.079). Discussion: IT is safe and feasible for children with obesity and holds promise for reducing dyspnea and improving healthy activity in children with obesity. Breathe-Fit trial NCT05412134.

Exploring the Feasibility and Acceptability of Providing Caregivers Who Formula-feed with Smaller Infant Bottles in a Primary Care Clinic

OBJECTIVES

Larger bottle size is associated with faster weight gain in infants, but little is known about acceptability and feasibility of providing bottles in primary care clinics.

METHODS

We randomized parent-infant dyads (N = 40) to receive a set of 4-ounce bottles or to continue using their own bottles. Demographic and anthropometric information were collected at enrollment and one follow-up visit 1-5 months later. The primary aim was to assess feasibility and acceptability of the intervention strategy. We compared components of bottle feeding, including usual bottle sizes used, number and volume of feeds with Wilcoxon rank-sum tests, and changes in weight-for-age and weight-for-length z-scores during the study period with t-tests, using p < 0.05 as an indicator of statistical significance.

RESULTS

Of participants randomized to receive bottles, 90% were using the 4oz bottles at follow up. The intervention group reported a significantly lower median bottle size (4oz) than the control group (8oz) at follow up, and parents reported acceptability and continued use of the bottles.

CONCLUSIONS FOR PRACTICE

An intervention to provide smaller bottles was feasible, mostly acceptable, resulted in lower median bottle size. Further research is needed to determine whether it represents a novel way to prevent rapid infant weight gain.

Infant Television Watching Predicts Toddler Television Watching in a Low-Income Population

OBJECTIVE

This study examines the development of active television (TV) watching behaviors across the first 2 years of life in a racially and ethnically diverse, low-income cohort and identifies caregiver and child predictors of early TV watching.

METHODS

We used longitudinal data from infants enrolled in the active control group (N = 235; 39% Latino; 29% Black; 15% White) of Greenlight, a cluster randomized multisite trial to prevent childhood obesity. At preventive health visits from 2 months to 2 years, caregivers were asked: "How much time does [child's first name] spend watching television each day?" Proportional odds models and linear regression analyses were used to assess associations among TV introduction age, active TV watching amount at 2 years, and sociodemographic factors.

RESULTS

Sixty-eight percent of children watched TV by 6 months, and 88% by 2 years. Age of TV introduction predicted amount of daily active TV watching at 2 years, with a mean time of 93 minutes if starting at 2 months; 64 minutes if starting at 4 or 6 months; and 42 minutes if starting after 6 months. Factors predicting earlier introduction included lower income, fewer children in household, care away from home, male sex, and non-Latino ethnicity of child.

CONCLUSIONS

Many caregivers report that their infants actively watch TV in the first 6 months of life. Earlier TV watching is related to sociodemographic factors yet predicts more daily TV watching at 2 years even controlling those factors. Interventions to limit early TV watching should be initiated in infancy.

A randomized controlled trial examining an exam room poster to prompt communication about weight

BACKGROUND

Recognition of childhood weight status is important to the adoption of healthy lifestyle behaviours.

OBJECTIVES

We assessed whether an exam room educational poster addressing weight and healthy lifestyle behaviours was acceptable to parents, prompted parent-provider communication or improved parental weight perception accuracy.

METHODS

In this multi-site randomized controlled trial, exam rooms were randomized to display the posters (English and Spanish) or not. Children ages 3 to 8 years (N = 965) attending well visits were weighed and roomed per usual clinic protocol. After the visit, parents completed a questionnaire assessing demographics, child weight status perceptions and whether they discussed weight status with provider or were shown growth charts. We used separate logistic regression analyses to examine associations between intervention status and: asking provider about child weight, being shown growth charts, and accuracy of weight perception, adjusting for covariates and clustering by exam room.

RESULTS

Of the parents who saw the poster, 97% liked seeing it and reported greater understanding of weight status visualization (96%) and healthy lifestyle behaviours (94%). Parents who saw the poster were more likely to report being shown a growth chart (OR 1.87, 95% 1.06, 3.30) but were not more likely to ask about their child's weight status nor accurately report their child's weight status.

CONCLUSIONS

An educational exam room poster about healthy weight was well-received by parents and prompted providers to show the child's growth chart but did not prompt parent-initiated conversations about weight status nor improve parental weight perception accuracy.

Concordance of Child and Parent Reports of Children's Screen Media Use

OBJECTIVE

Little is known about the concordance of parent and child reports of children's media consumption, even though parents are often asked to report for their children in clinical care settings. Our objective was to understand how parent and child reports of children's media consumption differ in an era of changing screen media consumption via personal devices.

METHODS

As part of a larger study about the reception of health-related cues from children's media, children ages 9 to 11 years (N = 114) and their parents independently completed identical questionnaires about specific media use and health behaviors. To examine concordance between child and parent reports of children's screen media use, we calculated the mean number of minutes per day and proportions reported by the child and parent and assessed concordance with t-tests and chi-square tests.

RESULTS

On a typical day, children reported nearly an hour each of video and app game use, computer use, and television exposure. Overall, child and parent reports were similar, usually within 10 minutes of each other; however, among 3 measures of TV use, parents consistently reported less TV exposure than children. There was significant discordance in the percentages of parents and children reporting the presence of a TV in the child's room.

CONCLUSIONS

Parent and child reports of children's media use were generally concordant; however, there were important disagreements, such as TV use in the child's room and during meals. We discuss possible causes of discrepancies and implications.

Obesogenic Behavior and Weight-Based Stigma in Popular Children's Movies, 2012 to 2015

BACKGROUND

Obesity-promoting content and weight-stigmatizing messages are common in child-directed television programming and advertisements, and 1 study found similar trends in G- and PG-rated movies from 2006 to 2010. Our objective was to examine the prevalence of such content in more recent popular children's movies.

METHODS

Raters examined 31 top-grossing G- and PG-rated movies released from 2012 to 2015. For each 10-minute segment (N = 302) and for movies as units, raters documented the presence of eating-, activity-, and weight-related content observed on-screen. To assess interrater reliability, 10 movies (32%) were coded by more than 1 rater.

RESULTS

The result of Cohen's κ test of agreement among 3 raters was 0.65 for binary responses (good agreement). All 31 movies included obesity-promoting content; most common were unhealthy foods (87% of movies, 42% of segments), exaggerated portion sizes (71%, 29%), screen use (68%, 38%), and sugar-sweetened beverages (61%, 24%). Weight-based stigma, such as a verbal insult about body size or weight, was observed in 84% of movies and 30% of segments.

CONCLUSIONS

Children's movies include much obesogenic and weight-stigmatizing content. These messages are not shown in isolated incidences; rather, they often appear on-screen multiple times throughout the entire movie. Future research should explore these trends over time, and their effects.

Implicit Weight Bias in Children Age 9 to 11 Years

OBJECTIVES

Assess implicit weight bias in children 9 to 11 years old.

METHODS

Implicit weight bias was measured in children ages 9 to 11 (N = 114) by using the Affect Misattribution Procedure. Participants were shown a test image of a child for 350 milliseconds followed by a meaningless fractal (200 milliseconds), and then they were asked to rate the fractal image as "good" or "bad." We used 9 image pairs matched on age, race, sex, and activity but differing by weight of the child. Implicit bias was the difference between positive ratings for fractals preceded by an image of a healthy-weight child and positive ratings for fractals preceded by an image of an overweight child.

RESULTS

On average, 64% of abstract fractals shown after pictures of healthy-weight children were rated as "good," compared with 59% of those shown after pictures of overweight children, reflecting an overall implicit bias rate of 5.4% against overweight children (P < .001). Healthy-weight participants showed greater implicit bias than over- and underweight participants (7.9%, 1.4%, and 0.3% respectively; P = .049).

CONCLUSIONS

Implicit bias toward overweight individuals is evident in children aged 9 to 11 years with a magnitude of implicit bias (5.4%) similar to that in studies of implicit racial bias among adults.

Polycyclic aromatic hydrocarbon and particulate emissions from two-stage combustion of polystyrene: the effect of the primary furnace temperature

A study is presented on laboratory-scale combustion of polystyrene (PS) to identify staged-combustion conditions that minimize emissions. Batch combustion of shredded PS was conducted in fixed beds placed in a bench-scale electrically heated horizontal muffle furnace. In most cases, combustion of the samples occurred by forming gaseous diffusion flames in atmospheric pressure air. The combustion effluent was mixed with additional air, and it was channeled to a second muffle furnace (afterburner) placed in series. Further reactions took place in the secondary furnace at a residence time of 0.7 s. The gas temperature of the primary furnace was varied in the range of 500-1,000 degrees C, while that of the secondary furnace was kept fixed at 1,000 degrees C. Sampling for CO, CO2, O2, soot, and unburned hydrocarbon emissions (volatile and semivolatile, by GC-MS) was performed at the exits of the two furnaces. Results showed that the temperature of the primary furnace, where PS gasifies, is of paramount importance to the formation and subsequent emissions of organic species and soot. Atthe lowesttemperatures explored, mostly styrene oligomers were identified at the outlet of the primary furnace, but they did not survive the treatment in the secondary furnace. The formation and emission of polycyclic aromatic hydrocarbons (PAH) and soot were suppressed. As the temperature in the first furnace was raised, increasing amounts of a wide range of both unsubstituted and substituted PAH containing up to at least seven condensed aromatic rings were detected. A similar trend was observed for total particulate yields. The secondary furnace treatment reduced the yields of total PAH, but it had an ambiguous effect on individual species. While most low molecular mass PAH were reduced in the secondary furnace, concentrations of some larger PAH increased under certain conditions. Thus, care in the selection of operating conditions of both the primary furnace (gasifier/ burner) and the secondary furnace (afterburner) must be exercised to minimize the emission of hazardous pollutants. The emissions of soot were also reduced in the afterburner but not drastically. This indicates that soot is indeed resistant to oxidation; thus, it would be best to avoid its formation in the first place. An oxidative pyrolysis temperature of PS in the vicinity of 600 degrees C appears to accomplish exactly that. An additional afterburner treatment at a sufficiently high temperature (1,000 degrees C) may be a suitable setting for minimization of most pollutants. To obtain deeper understanding of chemical processes, the experimental results were qualitatively compared with preliminary predictions of a detailed kinetic model that describes formation and destruction pathways of chemical species including most PAH observed in the present work. The modeling was performed forthe secondary furnace assuming plug-flow conditions therein. The experimentally determined chemical composition at the outlet of the primary furnace was part of the input parameters of the model calculation.

MgATP-Bound and nucleotide-free structures of a nitrogenase protein complex between the Leu 127 Delta-Fe-protein and the MoFe-protein

A mutant form of the nitrogenase iron protein with a deletion of residue Leu 127, located in the switch II region of the nucleotide binding site, forms a tight, inactive complex with the nitrogenase molybdenum iron (MoFe) protein in the absence of nucleotide. The structure of this complex generated with proteins from Azotobacter vinelandii (designated the L127Delta-Av2-Av1 complex) has been crystallographically determined in the absence of nucleotide at 2.2 A resolution and with bound MgATP (introduced by soaking) at 3.0 A resolution. As observed in the structure of the complex between the wild-type A. vinelandii nitrogenase proteins stabilized with ADP.AlF(4-), the most significant conformational changes in the L127Delta complex occur in the Fe-protein component. While the interactions at the interface between the MoFe-protein and Fe-proteins are conserved in the two complexes, significant differences are evident at the subunit-subunit interface of the dimeric Fe-proteins, with the L127Delta-Av2 structure having a more open conformation than the wild-type Av2 in the complex stabilized by ADP.AlF(4-). Addition of MgATP to the L127Delta-Av2-Av1 complex results in a further increase in the separation between Fe-protein subunits so that the structure more closely resembles that of the wild-type, nucleotide-free, uncomplexed Fe-protein, rather than the Fe-protein conformation in the ADP.AlF(4-) complex. The L127Delta mutation precludes key interactions between the Fe-protein and nucleotide, especially, but not exclusively, in the region corresponding to the switch II region of G-proteins, where the deletion constrains Gly 128 and Asp 129 from forming hydrogen bonds to the gamma-phosphate and activating water for attack on this group, respectively. These alterations account for the inability of this mutant to support mechanistically productive ATP hydrolysis. The ability of the L127Delta-Av2-Av1 complex to bind MgATP demonstrates that dissociation of the nitrogenase complex is not required for nucleotide binding.

Thermodynamic driving forces for PAH isomerization and growth during thermal treatment of polluted soils

For a limiting case of thermodynamic equilibrium, the importance of two classes of thermal chemical reactions that modify the structure and bioactivity of polycyclic aromatic hydrocarbons (PAH) was assessed computationally. These reactions are molecular weight (MW) growth by acetylene addition, and intramolecular rearrangement (isomerization). Temperatures (300-1100 degrees C), and the chemical environment (C(2)H(2)/H(2) molar ratios) were selected for relevancy to thermal treatment of PAH-contaminated soils under oxygen-free conditions. Molecular mechanics methods [MM3(92)] were used to compute thermochemical properties for calculation of equilibrium constants, i.e., heats of formation, standard entropies, and heat capacities for 30 PAH with empirical formulae C(14)H(10), C(16)H(10), C(18)H(10), C(18)H(12), C(20)H(10), and C(20)H(12). Included were 11 PAH containing only six-membered rings and 19 PAH containing both five- and six-membered rings. For each of these PAH the calculations predict that with increasing temperature, isomerization increases the "complexity" of the PAH mixture, i.e., the relative abundance of each PAH isomer in the mixture other than the most stable isomer, increases. Isomerization also partially transforms non-mutagens to mutagens, e.g., pyrene and benzo[e]pyrene to fluoranthene and benzo[a]pyrene, respectively, and partially converts cyclopenta[c, d]pyrene (CPEP) and chrysene, both human cell mutagens, to one and three additional human cell mutagens, respectively. Acetylene addition transforms the non-mutagens phenanthrene and pyrene to the mutagens triphenylene and CPEP, respectively. Some of the predicted PAH have been observed elsewhere among the products of aromatics pyrolysis. This study elucidates PAH reactivity for comparison with measurements, and identifies PAH reactions to be monitored and avoided in soil thermal decontamination and other waste remediation processes.

Nitrogenase: standing at the crossroads

Nitrogenase catalyzes the ATP-dependent reduction of dinitrogen to ammonia, which is central to the process of biological nitrogen fixation. Recent progress towards establishing the mechanism of action of this complex metalloenzyme reflects the contributions of a combination of structural, biochemical, spectroscopic, synthetic and theoretical approaches to a challenging problem with implications for a range of biochemical and chemical systems.

Chemical characterization and bioactivity of polycyclic aromatic hydrocarbons from non-oxidative thermal treatment of pyrene-contaminated soil at 250-1,000 degrees C

In this paper we report yields, identities, and mutagenicities of products from heating a polycyclic aromatic hydrocarbon (PAH)-contaminated, Superfund-related synthetic soil matrix without exogenous oxygen. We heated batch samples of soil pretreated with 5.08 wt% (by weight) pyrene in a tubular furnace under a constant flow of helium gas at 250, 500, 750, and 1,000 +/- 20 degrees C. Dichloromethane (DCM) extracts of cooled residues of heated soil and of volatiles condensed on a cold finger after 1 sec residence time at furnace temperature were assayed gravimetrically and analyzed for PAH by HPLC, HPLC coupled to mass spectrometry, and gas chromatography coupled to mass spectrometry. All four temperatures volatilized pyrene and generated other PAHs, including alkylated pyrenes. We detected bioactive PAHs in the product volatiles: cyclopenta[cd]pyrene (CPP) at 750 and 1,000 degrees C and benzo[a]pyrene (BaP) at 1,000 degrees C. We found a clean soil residue, i.e., no pyrene or other DCM extracts, only at 750 degrees C. Control experiments with uncontaminated soil, pyrene, and Ottawa sand plus 4.89 wt% pyrene revealed no CPP or BaP production from soil itself, but these experiments imply that pyrene interactions with soil, e.g., soil-bound silica, stimulate CPP and BaP production. We detected mutagenicity to human diploid lymphoblasts (in vitro) in volatiles from 1,000 degrees C heating of soil plus pyrene and sand plus pyrene, and in the residue from 500 degrees C heating of soil plus pyrene. Three plausible pathways for pyrene conversion to other PAHs are a) a reaction with light gas species, e.g., soil- or pyrene-derived acetylene; b) loss of C(2)-units followed by reaction with a PAH; and c) dimerization with further molecular weight growth via cyclodehydrogenation. This study shows that thermal treatment of PAH-polluted soil may generate toxic by-products that require further cleanup by oxidation or other measures.

The nursing home medical director and quality care

Years of experience show that improving nursing home care through the continuing supervision of physicians raises issues that are not easily resolved. Quality medical care is a must and the authors, an administrator and a physician, give specific examples for involvement by the medical director.

Structural bioenergetics and energy transduction mechanisms

Life depends on transduction processes that couple cellular metabolism to environmental energy sources such as light or reduced compounds. These primary energy sources must be efficiently converted into forms that can be utilized by cells for biosynthesis, motility, transport, regulation, and other metabolic functions. In recent years, there has been an explosive increase in the determination of structures for proteins mediating energy transduction processes. These developments provide the opportunity to evaluate the structural basis for the efficient coupling of two energetic processes, which defines the area of structural bioenergetics. Here, we present some general features of energy transduction processes, including arguments that effective coupling of two processes by a transduction protein occurs by way of conformational states that are common to the catalysis of each process. This is illustrated by examples from the nucleotide switch family of proteins, with emphasis on the nitrogenase system where ATP hydrolysis is coupled to an electron transfer reaction.

Secondary structure extensions in Pyrococcus furiosus ferredoxin destabilize the disulfide bond relative to that in other hyperthermostable ferredoxins. Global consequences for the disulfide orientational heterogeneity

The single cubane cluster ferredoxin (Fd) from the hyperthermophilic archaeon Pyrococcus furiosus (Pf) possesses several unique properties when compared even to Fds from other hyperthermophilic archaea or bacteria. These include an equilibrium molecular heterogeneity, a six- to seven-residue increase in size, an Asp rather than the Cys as one cluster ligand, and a readily reducible disulfide bond. NMR assignments and determination of both secondary structure and tertiary contacts remote from the paramagnetic oxidized cluster of Pf 3Fe Fd with an intact disulfide bond reported previously (Teng Q., Zhou, Z. H., Smith, E. T., Busse, S. C., Howard, J. B. Adams, M. W. W., and La Mar, G. (1994) Biochemistry 33, 6316-6328) are extended here to the 4Fe oxidized cluster WT (1H and 15N) and D14C (1H only) Fds with an intact disulfide bond and to the 4Fe oxidized WT Fd (1H and 15N) with a cleaved disulfide bond. All forms are shown to possess a long (13-member) alpha-helix, two beta-sheets (one double-, one triple-stranded), and three turns outside the cluster vicinity, each with tertiary contacts among themselves as found in other Fds. While the same secondary structural elements, with similar tertiary contacts, are found in other hyperthermostable Fds, Pf Fd has two elements, the long helix and the triple-stranded beta-sheet, that exhibit extensions and form multiple tertiary contacts. All Pf Fd forms with an intact disulfide bond exhibit a dynamic equilibrium heterogeneity which is shown to modulate a hydrogen-bonding network in the hydrophobic core that radiates from the Cys21-Cys48 disulfide bond and encompasses residues Lys36, Val24, Cys21, and Cys17 and the majority of the long helix. The heterogeneity is attributed to population of the alternate S and R chiralities of the disulfide bond, each destabilized by steric interactions with the extended alpha-helix. Comparison of the chemical shifts and their temperature gradients reveals that the molecular structure of the protein with the less stable R disulfide resembles that of the Fd with a cleaved disulfide bond. Both cluster architecture (3Fe vs 4Fe) and ligand mutation (Cys for Asp14) leave the disulfide orientational heterogeneity largely unperturbed. It is concluded that the six- to seven-residue extension that results in a longer helix and larger beta-sheet in Pf Fd, relative to other hyperthermostable Fds, more likely serves to destabilize the disulfide bond, and hence make it more readily reducible, than to significantly increase protein thermostability.

Thermal removal of pyrene contamination from soil: basic studies and environmental health implications

Effects of temperature (400-1000 degrees C) and rate of heating to 550 degrees C (100, 1000, 5000 degrees C/sec) on reduction of pyrene contamination in a Superfund-related soil and on yields of volatile products (tars, CO, CO2, methane, acetylene, ethylene) have been measured. Fifty (+/- 3)-milligram thin layers (less than or equal to 150 micron) of 63- to 125-micron soil particles, neat (i.e., without exogenous chemicals), or pretreated with 4.75 wt% of pyrene, were heated for about 1 to 6 sec, under 3 psig (pounds per in.(2) gauge) of helium in a 12-liter sealed chamber. Pyrene removal, defined as the difference in weight loss of neat versus contaminated soil, was virtually immune to heating rate but increased strongly with increasing temperature, approaching 100% at about 530 degrees C. However, for pyrenepolluted soil, excess soil weight loss and modified CO yields were observed above about 500 degrees C for a 1000 degrees C/sec heating rate. These observations suggest that soil chemical reactions with pyrene or pyrene decomposition products augment soil volatilization. Consequently at elevated temperatures, the difference in weight loss protocol may overestimate polycyclic aromatic hydrocarbon (PAH) removal from soil. Increasing heating rate caused yields of CO, CO(2), and acetylene from pyrene-polluted soil to pass through maxima. Heating neat or contaminated soil resulted in at least two gaseous products of particular environmental interest:acetylene, a precursor to PAH in thermal synthesis, and CO, a toxin to human hemoglobin.

Conformational variability in structures of the nitrogenase iron proteins from Azotobacter vinelandii and Clostridium pasteurianum

The nitrogenase iron (Fe) protein performs multiple functions during biological nitrogen fixation, including mediating the mechanistically essential coupling between ATP hydrolysis and electron transfer to the nitrogenase molybdenum iron (MoFe) protein during substrate reduction, and participating in the biosynthesis and insertion of the FeMo-cofactor into the MoFe-protein. To establish a structural framework for addressing the diverse functions of Fe-protein, crystal structures of the Fe-proteins from Azotobacter vinelandii and Clostridium pasteurianum have been determined at resolutions of 2.2 A and 1.93 A, respectively. These two Fe-proteins are among the more diverse in terms of amino acid sequence and biochemical properties. As described initially for the A. vinelandii Fe-protein in a different crystal form at 2.9 A resolution, each subunit of the dimeric Fe-protein adopts a polypeptide fold related to other mononucleotide-binding proteins such as G-proteins, with the two subunits bridged by a 4Fe:4S cluster. The overall similarities in the subunit fold and dimer arrangement observed in the structures of the A. vinelandii and C. pasteurianum Fe-proteins indicate that they are representative of the conformation of free Fe-protein that is not in complex with nucleotide or the MoFe-protein. Residues in the cluster and nucleotide-binding sites are linked by a network of conserved hydrogen bonds, salt-bridges and water molecules that may conformationally couple these regions. Significant variability is observed in localized regions, especially near the 4Fe:4S cluster and the MoFe-protein binding surface, that change conformation upon formation of the ADP.AlF4- stabilized complex with the MoFe-protein. A core of 140 conserved residues is identified in an alignment of 59 Fe-protein sequences that may be useful for the identification of homologous proteins with functions comparable to that of Fe-protein in non-nitrogen fixing systems.

Risk status and home intervention among children with failure-to-thrive: follow-up at age 4

Examined the moderating effects of risk status on the impact of home intervention in a follow-up study of children with failure-to-thrive (FTT). Two types of risk (demographic and maternal negative affectivity) and two levels of intervention were examined. In this randomized clinical trial, all children received services in a multidisciplinary growth and nutrition clinic, and half the children also received home visits from a lay home visitor for 1 year. There were no effects of demographic risk, maternal negative affectivity, or intervention status on child outcome at the close of the home intervention. However, at age 4, more than 1 year after the home intervention ended, there were effects of the home intervention on motor development among all children and on cognitive development and behavior during play among children of mothers who reported low levels of negative affectivity. Results highlight the importance of conducting follow-up assessments in the evaluation of home intervention services, and suggest that among low-SES families of children with FTT, home intervention may be most useful among mothers with low negative affectivity.

Structure of ADP x AIF4(-)-stabilized nitrogenase complex and its implications for signal transduction

The coupling of ATP hydrolysis to electron transfer by the enzyme nitrogenase during biological nitrogen fixation is an important example of a nucleotide-dependent transduction mechanism. The crystal structure has been determined for the complex between the Fe-protein and MoFe-protein components of nitrogenase stabilized by ADP x AIF4-, previously used as a nucleoside triphosphate analogue in nucleotide-switch proteins. The structure reveals that the dimeric Fe-protein has undergone substantial conformational changes. The beta-phosphate and AIF4- groups are stabilized through intersubunit contacts that are critical for catalysis and the redox centre is repositioned to facilitate electron transfer. Interactions in the nitrogenase complex have broad implications for signal and energy transduction mechanisms in multiprotein complexes.

Aluminum fluoride inhibition of nitrogenase: stabilization of a nucleotide.Fe-protein.MoFe-protein complex

Coupling of ATP hydrolysis to electron transfer in nitrogenase has properties similar to nucleotide-dependent switch proteins. Aluminum fluoride, a powerful inhibitor of some switch proteins, is a progressive, slowly reversible (t1/2 for reversal > 21 h) inhibitor of nitrogenase that requires both component proteins (Fe-protein and MoFe-protein) and nucleotide (either ATP or ADP). The pseudo first-order inhibition is dependent on the aluminum fluoride species, AlF4, and is linear with [Al] concentration (nonsaturating) at a pH optimum near 7.1-7.3. The inhibitor appears to react with the transient complex of the two component proteins and nucleotide. Although ADP can support the AlF inhibition, the rate of inhibition is more than 30-fold greater with ATP, which suggests the reactive conformation more closely resembles ATP hydrolysis. Conditions that increase enzymic turnover (protein concentration and component ratio) also increase the rate of inhibition, while ionic strength which slows enzymic activity spares the inhibition. The inhibited protein was isolated by gel filtration chromatography and found to be an AlF4-ADP-Fe-protein.MoFe-protein complex with the ratio of 2:1 that is consistent with two active sites per MoFe-protein alpha 2 beta 2 tetramer. Hence, inhibition by AlF4 is the stabilization of a complex that no longer hydrolyzes ATP or reduces substrates. We propose that AlF-ADP is tightly bound only in Fe-protein conformations obtained in the complex with MoFe-protein. Ligands (including Arg-46) at the base of a flexible flap on the Fe-protein could immobilize MoFe-protein--Fe-protein interface, thereby preventing dissociation of the complex.

Characterization of flame-generated C10 to C 160 polycyclic aromatic hydrocarbons by atmospheric-pressure chemical ionization mass spectrometry with liquid introduction via heated nebulizer interface

Complex mixtures of polycyclic aromatic hydrocarbons (PAHs) generated from fuel-rich combustion of ethylene-naphthalene mixtures in a jet-stirred-plug-flow reactor were chemically characterized by combined mass spectrometric techniques to yield product composition data that cover the molecular mass region from simple PAHs (naphthalene, 128 u) to large molecules comparable in molecular size (1792 u) to nanoparticles of soot. Two techniques based on atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) were investigated: (1) APCI-MS combined with high-performance liquid chromatography through a heated nebulizer interface was found suitable for PAHs up to C36 (448 u). (2) For the characterization of larger PAHs beyond C36, direct liquid introduction (DLI) of sample into an atmospheric-pressure chemical ionization mass spectrometer through a heated nebulizer gave protonated molecular ions for PAHs over the m/z 400-2000 range. Although unequivocal elemental composition information is unattainable from the unit-resolution DLI/APCI-MS data, by starting with structural data from identified C16 to C32 PAHs, and applying PAH molecular growth principles, it was possible to generate PAH molecular maps from the DLI/APCI-MS data from which values for the elemental composition could be derived for all major peaks.

Participation of the disulfide bridge in the redox cycle of the ferredoxin from the hyperthermophile Pyrococcus furiosus: 1H nuclear magnetic resonance time resolution of the four redox states at ambient temperature

The oxidized and reduced forms of the [4Fe-4S]-containing ferredoxin from the hyperthermophilic archaeon Pyrococcus furiosus, Pf, have been investigated by 1H nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy and thiol titrations. We have identified and isolated at Ambient temperature four distinct redox states for the [4Fe-4S] form of the ferredoxin. These states differ in the redox state of the cluster, which is coordinated by Cys 11, Asp 14, Cys 17, and Cys 56, and of a disulfide bridge between Cys 21 and Cys 48. The protein, as isolated under anaerobic conditions, designated 4Fe FdBred, contains the reduced cluster and two free thiols. The cluster, but not the thiols, is readily oxidized by brief exposure to O2 to yield 4Fe FdBOX. Prolonged O2 treatment (> 24 h at 30 degrees C) is required to generate the protein with a disulfide (4Fe FdAOX) while this fully oxidized form is readily converted by brief reduction with sodium dithionite to the protein with a reduced cluster and a disulfide (4Fe FdAred). Analyses of the magnitude and the number of hyperfine-shifted resonances in each of the four redox states are discussed.

Solution 1H NMR determination of secondary structure for the three-iron form of ferredoxin from the hyperthermophilic archaeon Pyrococcus furiosus

Two-dimensional 1H NMR data have been used to make sequence-specific assignments and define the secondary structure of the three-iron form of the oxidized ferredoxin, Fd, from the hyperthermophilic archaeon Pyrococcus furiosus, Pf. Signals for at least some protons were located for 65 of the 66 amino acids in the sequence, in spite of the paramagnetic (S = 1/2) ground state, but not all could be assigned. Unassigned and missing signals could be qualitatively correlated with the expected proximity of the protons to the paramagnetic cluster. The secondary structure was deduced from qualitative analysis of the 2D nuclear Overhauser effect, which identified two antiparallel beta-sheets, one triple-stranded including Ala1-Ser5, Val39-Glu41, and Thr62-Ala66, and one double-stranded consisting of Glu26-Asn28 and Lys32-Glu34, as well as an alpha-helix involving Glu43-Glu54. Three tight type I turns are located at residues Asp7-Thr10, Pro22-Phe25, and Asp29-Gly31. Comparison with the crystal structure of Desulfovibrio gigas, Dg, Fd (Kissinger et al., 1991) reveals a very similar folding topology, although several secondary structural elements are extended in Pf relative to Dg Fd. Thus the beta-sheet involving the two termini is expanded to include the two terminal residues and incorporates a third strand from the internal loop that is lengthened by several insertions in Pf relative to Dg Fd. The double-stranded beta-sheet in the interior of Pf Fd is lengthened slightly due to a much tighter type I turn between the two strands. The helix near the C-terminus is three residues longer in Pf than in Dg Fd, as well as being shifted toward the N-terminus. The disulfide link between the two nonligating Cys residues (Cys21 and Cys48) is conserved in Pf Fd, but the link near the C-terminus is in the middle of the long alpha-helix in Pf Fd, instead of at the N-terminus of the helix as in Dg Fd. The extensions of the beta-sheets and alpha-helix increase the number of main-chain hydrogen bonds in Pf Fd by approximately 8 relative to those in Dg Fd and likely contribute to its remarkable thermostability (it is unaffected by anaerobic incubation at 95 degrees C for 24 h).(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of a cell surface glycoprotein associated with maturation of rat spermatozoa

The principal galactose oxidase/NaB[3H]4-labeled membrane protein of rat caudal epididymal spermatozoa was isolated by hydrophobic interaction chromatography. The protein is released from the membrane by the action of phosphatidylinositol specific phospholipase C, and thereby its properties are transformed from those of a protein anchored to the hydrophobic membrane to those of a hydrophilic solution protein. Because it is the only membrane-associated protein released by the enzyme which did not absorb to a propylaspartate resin, a simple, single step purification procedure was devised. Although the amino terminus of the protein is blocked to Edman degradation, the majority of the protein structure was determined from a series of tryptic peptides and from limited acid hydrolysis. Approximately 65% of the protein mass is carbohydrate which is primarily attached through O-glycosidic bonds to the 18 threonines. The molecular weight of the glycoprotein was estimated to be 16,600, considerably smaller than the M(r) = 26,000 to 37,000 previously determined by gel electrophoresis. The anomalous electrophoretic behavior is undoubtedly due to the large percentage of carbohydrate. The distribution of carbohydrate on the protein side chains suggests the protein may form a positively charged, specialized scaffolding for the presentation of the carbohydrate moieties. Because the appearance of the ability to label the protein with galactose oxidase is correlated with sperm maturation in the epididymis, the glycoprotein structures may be an important component in the fertilization process. The combination of linkage by glycosylphosphatidylinositol and low molecular weight mucin-like structure indicates this may be a member of a new class of membrane proteins.

Nucleotide-iron-sulfur cluster signal transduction in the nitrogenase iron-protein: the role of Asp125

Electron transfer in nitrogenase involves a gating process initiated by MgATP (magnesium adenosine triphosphate) binding to Fe-protein. The redox site, an 4Fe:4S cluster, is structurally separated from the MgATP binding site. For MgATP hydrolysis to be coupled to electron transfer, a signal transduction mechanism is proposed that is similar to that in guanosine triphosphatase proteins. Based on the three-dimensional structure of Fe-protein, Asp125 is likely to be part of a putative transduction path. Altered Fe-protein with Glu replacing Asp has been prepared and retains the ability for the initial nucleotide-dependent conformational change. However, either MgADP or MgATP can induce the shift and Mg binding to the nucleotide is no longer essential.

Proton NMR investigation of the oxidized three-iron clusters in the ferredoxins from the hyperthermophilic archae Pyrococcus furiosus and Thermococcus litoralis

The 3Fe forms of ferredoxins (Fd) from the hyperthermophilic archaebacteria Pyrococcus furiosus (Pf) and Thermococcus litoralis (Tl) have been investigated by 1H NMR. A combination of one-dimensional nuclear Overhauser and two-dimensional NOESY and bond correlation spectroscopy provides the assignment of the aromatic residues, one conserved valine, and the location of the signals for each of the three cysteines coordinated to the clusters. Dipolar contacts between the Trp 2 and Tyr 46 in Pf Fd and from an invariant phenylalanine to an invariant valine and a cluster cysteine in both Fd confirm a folding pattern for these proteins that is very similar to that of the crystallographically characterized ferredoxin from the mesophile Desulfovibro gigas. The sequence-specific assignment of the buried cysteine near the invariant phenylalanine has been made. The temperature dependence of the contact-shifted cysteinyl residues reveals a distinct 2:1 asymmetry in the magnetic coupling among the three high-spin ferric ions, in that one cysteine exhibits Curie behavior, while the other two cysteines display anti-Curie behavior. These magnetic properties are rationalized qualitatively on the basis of a magnetic coupling scheme where two iron couple to yield an intermediate spin of 2 which couples to the remaining S = 5/2 iron to yield the total cluster spin 1/2. This magnetic asymmetry appears to be a characteristic feature of oxidized 3 Fe clusters. Pf Fd also undergoes a dynamic equilibrium between two alternate forms that differ slightly in the environment of two of the coordinated cysteines. Analysis of the pattern of the contact shifts for the three cysteines in the two ferredoxins suggests that the cysteine coordinated to the unique iron does not have the same sequence origin.

Ionic interactions in the nitrogenase complex. Properties of Fe-protein containing substitutions for Arg-100

A series of Azotobacter vinelandii strains have been constructed in which the nitrogenase Fe-protein (Av2) was altered by substitutions for Arg-100. This invariant residue is a likely partner in a salt bridge with the MoFe-protein and, in some species, is the site of reversible regulation by ADP-ribosylation (Pope, M. R., Murrell, S. A., and Ludden, P. W. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 3173-3177). Although we find that arginine is the optimum amino acid, other residues in this position could support diazotrophic growth. These results were surprising because Klebsiella pneumoniae Fe-protein substituted by His-100 had been reported to be inactive (Lowery, R. G., Chang, C. L., Davis, L. C., McKenna, M.-C., Stevens, P. J., and Ludden, P. W. (1989) Biochemistry 28, 1206-1212). Two altered Fe-proteins (Av2-R100Y, the tyrosyl form, and Av2-R100H, the histidyl form) were isolated and, in contrast to this earlier report, we found that both had some activity in acetylene reduction. However, both altered proteins exhibited a decreased maximum velocity (35 and 3% of wild type, respectively) and were strongly inhibited by excess MoFe-protein. These adverse activity parameters were also manifest in the increased sensitivity of the altered proteins to inhibition by salts. Indeed, the salt sensitivity of Av2-R100H is so significant that its activity is masked in the normal assay and is easily missed. In addition, for Av2-R100H, substrate reduction is substantially uncoupled from MgATP hydrolysis. These results suggest that substitutions for Arg-100 may decrease the affinity of the Fe-protein for the MoFe-protein prior to electron transfer but increase affinity after electron transfer. Hence, the role of Arg-100 may be to provide the optimum balance in stabilities of these two complexes for maximum efficiency in substrate reduction.

Two-dimensional NMR investigation of iron-sulfur cluster electronic and molecular structure of oxidized Clostridium pasteurianum ferredoxin. Interpretability of contact shifts in terms of cysteine orientation

A two-dimensional NMR study has been carried out on the four-iron clusters of a bacterial oxidized ferredoxin for the purpose of investigating the relationship between contact shift patterns and the orientation of the individual coordinated cysteines. The ferredoxin from Clostridium pasteurianum, CpFdox, was selected because of its extensive sequence homology, and likely close structural similarity, to the crystallographically characterized ferredoxin from Peptococcus aerogenes, Pa Fdox (Adman, E.T., Sieker, L.C., and Jensen, L. H. (1973) J. Biol. Chem. 248, 3987-3996). Rapid data collection rates with minimal but adequate acquisition time allowed the detection of numerous CpFdox cross-peaks from the contact-shifted and strongly relaxed coordinated cysteinyl C beta H protons in the resolved 10-20 ppm window. Relatively strong magnitude COSY cross peaks from the resolved eight cysteinyl C beta H resonance unambiguously locate the geminal C beta H partner for each residue; weaker cross-peaks locate the C alpha Hs from three of the residues. The geminal nature of the magnitude-COSY detected partners to the resolved C beta H peaks is confirmed by strong NOESY cross-peaks. The NOESY spectra, moreover, assign an additional two cysteinyl C alpha H resonances. The present results confirm some previous one-dimensional NOE assignments, revise others, and locate resonances previously undetected (Bertini, I., Briganti, F., Luchinat, C., and Scozzafara, A. (1990) Inorg. Chem. 29, 1874-1880). A striking pairwise pseudo-symmetry in cysteinyl contact shift patterns is observed which is attributed to the previously recognized pseudo-symmetry in the crystal of PaFdox. A detailed analysis of the structural/electronic determinants of the coordinated cysteine C beta H contact shift pattern is made, and the NMR data necessary for unique interpretation are identified. It is shown that analysis of the relaxation properties of cysteine beta-methylene protons provides the stereospecific assignments necessary for comparison of shift ratios with crystallographic structural data. The available structural data on PaFdox (Backes, G., Mino, Y., Loehr, T., Meyer, T., Cusanovich, M., Sweeney, W., Adman, E., and Sanders-Loehr, J. (1991) J. Am. Chem. Soc. 13, 2055-2064) are qualitatively but not quantitatively consistent with the observed cysteinyl contact shift pattern, with the NMR data reflecting more asymmetry than previous studies. A tentative assignment of a single pair of symmetry-related cysteines is proposed.(ABSTRACT TRUNCATED AT 400 WORDS)

Determinants of protein hyperthermostability: purification and amino acid sequence of rubredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus and secondary structure of the zinc adduct by NMR

The purification, amino acid sequence, and two-dimensional 1H NMR results are reported for the rubredoxin (Rd) from the hyperthermophilic archaebacterium Pyrococcus furiosus, an organism that grows optimally at 100 degrees C. The molecular mass (5397 Da), iron content (1.2 +/- 0.2 g-atom of Fe/mol), UV-vis spectrophotometric properties, and amino acid sequence (60% sequence identity with Clostridium pasteurianum Rd) are found to be typical of this class of redox protein. However, P. furiosus Rd is remarkably thermostable, being unaffected after incubation for 24 h at 95 degrees C. One- and two-dimensional 1H nuclear magnetic resonance spectra of the oxidized [Fe(III)Rd] and reduced [Fe(II)Rd] forms of P. furiosus Rd exhibited substantial paramagnetic line broadening, and this precluded detailed 3D structural studies. The apoprotein was not readily amenable to NMR studies due to apparent protein oxidation involving the free cysteine sulfhydryls. However, high-quality NMR spectra were obtained for the Zn-substituted protein, Zn(Rd), enabling detailed NMR signal assignment for all backbone amide and alpha and most side-chain protons. Secondary structural elements were determined from qualitative analysis of 2D Overhauser effect spectra. Residues A1-K6, Y10-E14, and F48-E51 form a three-strand antiparallel beta-sheet, which comprises ca. 30% of the primary sequence. Residues C5-Y10 and C38-A43 form types I and II amide-sulfur tight turns common to iron-sulfur proteins. These structural elements are similar to those observed by X-ray crystallography for native Rd from the mesophile C. pasteurianum. However, the beta-sheet domain in P. furiosus Rd is larger than that in C. pasteurianum Rd and appears to begin at the N-terminal residue. From analysis of the secondary structure, potentially stabilizing electrostatic interactions involving the charged groups of residues Ala(1), Glu(14), and Glu(52) are proposed. These interactions, which are not present in rubredoxins from mesophilic organisms, may prevent the beta-sheet from "unzipping" at elevated temperatures.

Fullerenes C60 and C70 in flames

The fullerenes C60 and C70 were first identified in carbon vapour produced by laser irradiation of graphite, and have recently been produced in macroscopic quantities by vaporization of graphite with resistive heating. It has also been suggested that fullerenes might be formed in sooting flames, and indeed all-carbon ions with mass/charge ratios suggestive of fullerenes have been detected in flames. These species were assumed to have the cage structures of fullerenes, but the mass spectroscopic evidence could not establish this conclusively. We have now collected samples of condensible compounds and soot from hydrocarbon combustion under a range of conditions, and analysed these using conventional techniques in an effort to detect fullerenes. Spectroscopic studies reveal the presence of C60 and C70 in yields and ratios that depend on temperature, pressure, carbon/oxygen ratio and residence time in the flame. Control of these conditions allows optimal yields of 3 g of fullerenes per kilogram of fuel carbon burned, and variation of the C70/C60 ratio over the range 0.26-5.7.

Cross-linking site in Azotobacter vinelandii complex

The Fe-protein and the MoFe-protein of the Azotobacter vinelandii nitrogenase complex can be chemically cross-linked by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (Willing, A., Georgiadis, M.M., Rees, D. C., and Howard, J. B. (1989) J. Biol. Chem. 264, 8499-8503). In this reaction, one of the identical subunits of the Fe-protein dimer is linked by an isopeptide bond to each beta-subunit of the MoFe-protein tetramer. The reaction has been found to be highly specific with greater than 85% of amino acid residues Glu-112 (Fe-protein) and Lys-399 (MoFe-protein) cross-linked to each other. Although Glu-112 is located in a highly conserved amino acid sequence, it is found in only half of the known Fe-protein sequences. Likewise, Lys-399 is not a conserved residue in the MoFe-protein. Glu-112 appears to be part of an anionic cluster of nine carboxylic acids which is located between the proposed thiol ligands for the Fe:S center. In contrast, the basic residue cluster which includes Lys-399 has been found in only in the Azotobacter MoFe-protein. Thus, this crosslinking reaction either is unique to Azotobacter nitrogenase or must involve other residues in the MoFe-protein of other species. Because Lys-399 and Glu-112 form a specific cross-link, it is probable that they are part of the interaction site leading to productive complex formation. This information should be useful for the model building of the complex from the crystallographic structures of the individual components.

Effect of salts on Azotobacter vinelandii nitrogenase activities. Inhibition of iron chelation and substrate reduction

The effect of salts on the catalytic activity of the molybdenum-containing nitrogenase complex from Azotobacter vinelandii has been investigated. NaCl was found to inhibit the reduction of the substrates, protons, acetylene, and dinitrogen by a common mechanism. The pattern of inhibition is sigmoidal, indicating a highly cooperative interaction involving multiple inhibitor sites. Sixteen other salts that were investigated also exhibited this pattern of inhibition. NaCl functions as a dead-end inhibitor without altering the number of MgATP hydrolyzed/electron transferred to substrate. The level of expressed inhibition is sensitive to MgATP concentration, the molar ratio of the MoFe-protein (Av1) to the Fe-protein (Av2), and total protein concentration. In addition, NaCl is an inhibitor of the MgATP-dependent, iron chelation of Av2. Although the inhibition is exhibited over the same salt concentration range as that for inhibition of substrate reduction, the pattern of inhibition is hyperbolic. A model based upon simple equilibrium interactions among the enzyme species, nucleotides, and inhibitor has been developed which quantitatively accounts for the observed effects of salt. In this model, the formation of the active complex between Av1 and Av2 is abolished by salts. Likewise, the apparent affinity of Av2 for MgATP is reduced. An additional prediction based upon the model is that the affinity between Av2 and Av1 is independent of nucleotide binding.

Cysteine labeling studies of beef heart aconitase containing a 4Fe, a cubane 3Fe, or a linear 3Fe cluster

The reactivity of cysteines following cluster destruction by iron chelation was investigated for [4Fe-4S]2+ and cubane [3Fe-4S]+ beef heart aconitase. When the chelator orthobathophenanthroline disulfonate was used, the formation of sulfur-sulfur bonds and the retention of inorganic sulfur from the cluster was observed. For both the 4Fe and 3Fe forms of aconitase, the two cysteines in peptide 7, the cysteine in peptide 3, and the cysteine in peptide 2 were found as the primary constituents of sulfur-sulfur bonds (the peptide sequences and nomenclature are from Plank, D. W., and Howard, J. B. (1988) J. Biol. Chem. 263, 8184-8189). Three of these four cysteines (peptides 3 and 7) correlated with those proposed to be cluster ligands recently determined by x-ray crystallography (Robbins, A. H. and Stout, C. D. (1989) Proteins, in press; Robbins, A. H., and Stout, C. D.,, (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 3639-3643) for pig heart aconitase. A mechanism is proposed whereby the greater affinity of orthobathophenanthroline disulfonate for Fe2+ relative to Fe3+ shifts the equilibrium toward reduction of ferric iron through sulfur-sulfur bond formation at the cluster site. Aconitase which has been oxidized with ferricyanide and from which the cluster iron has been removed by EDTA has been shown to have two di- or polysulfides (Kennedy, M. C., and Beinert, H. (1988) J. Biol. Chem. 263, 8194-8198). The cysteines found in the sulfur-sulfur bonds generated by this treatment also were predominantly those from peptides 3 and 7. In addition, the putative thiol ligands for the linear [3Fe-4S]+ cluster of aconitase are reported. The four cysteines of peptides 7 and 9 (two in each peptide) were found to be protected by the cluster from alkylation when the protein was denatured. The difference in the ligands between the cubane and linear forms indicates that a specific thiol exchange occurs during the conversion.

Structural organization of the lens fiber cell plasma membrane protein MP18

The 18,000-dalton bovine lens fiber cell intrinsic membrane protein MP18 was phosphorylated on a serine residue by both cAMP-dependent protein kinase and protein kinase C. In addition, this protein bound calmodulin and was recognized by a monoclonal antibody (2D10). These different regions were localized using enzymatic and chemical fragmentation of electrophoretically purified MP18 that had been phosphorylated with either cAMP-dependent protein kinase or protein kinase C. Partial digestion of 32P-labeled MP18 with protease V8 resulted in a Mr = 17,000 peptide that bound calmodulin, but neither contained 32P or was recognized by the monoclonal antibody 2D10. Furthermore, the 17-kDa peptide had the same N-terminal amino acid sequence as MP18. Thus, the monoclonal antibody 2D10 recognition site and the protein kinase phosphorylation site(s) are close together and confined to a small region in the C terminus of MP18. This conclusion was confirmed in experiments where MP18 was fragmented with trypsin, endoproteinase Lys-C, or CNBr. The location of the phosphorylation site was confirmed by sequencing the small 32P-labeled, C-terminal peptide that resulted from protease V8 digestion of 32P-labeled MP18. This peptide contained a consensus sequence for cAMP-dependent protein kinase.

Identification of an 18,000-dalton protein in mammalian lens fiber cell membranes

Monoclonal antibodies have been produced against electrophoretically purified MP18, a major calf lens membrane Mr = 18,000 substrate for cAMP-dependent protein kinase. One of these antibodies (monoclonal antibody 2D10) cross-reacted with both native MP18 in lens membranes, and sodium dodecyl sulfate-denatured, electrophoretically purified MP18. In immunoblots, this antibody recognized MP18 in pig, sheep, rat, human, but not chicken lens membranes, indicating the similarity of this protein in mammalian lenses. Amino acid sequencing revealed that the N-terminal sequence of MP18 is identical in these five different mammalian species and is unrelated to any previously sequenced lens or junctional proteins. Electron microscopic examination of monoclonal antibody 2D10-labeled bovine, pig and rat lens membranes indicated that MP18 is localized exclusively to the thicker 16-17 nm junctions in isolated preparations of lens fiber cell membranes. These results provide evidence of a role for MP18 in mammalian lens fiber cell junctional organization.

Fe:S cluster ligands are the only cysteines required for nitrogenase Fe-protein activities

Serine substitutions for the five conserved cysteins (residues 38, 85, 97, 132, and 184) have been made in the Azotobacter vinelandii nitrogenase Fe-protein by site-specific mutagenesis. At least moderate levels of enzyme activity (greater than 10% of wild type enzyme) were found for enzymes with serine substitutions at residues 38, 85, and 184; whereas, no activity was detected for enzymes with serines at residues 97 and 132. This is consistent with cysteines 97 and 132 being the four ligands to the Fe:S cluster (two ligands from each of the two identical subunits). Although previous chemical modification studies had implicated these residues as ligands, the earlier results did not portend the new finding that of all the conserved cysteines only these 2 residues are required for a second function of the Fe-protein. Namely, if either cysteine 97 or 132 is replaced, it appears that a functional Fe:S cluster cannot be incorporated into the apo-Fe-protein. The consequence is that these altered Fe-proteins cannot participate either in substrate reduction or in the biosynthesis of FeMo-cofactor, a metallocofactor of the MoFe-protein. These results implicate the Fe:S center of Fe-protein in the biosynthesis mechanism as either a redox partner or Fe:S donor. Additional results suggest that the posttranslational modification of Fe-protein by nifM product is not the insertion of the Fe:S center.

Iron-sulfur clusters of hydrogenase I and hydrogenase II of Clostridium pasteurianum

The iron and acid-labile sulfide contents and the electron paramagnetic resonance (EPR) properties of hydrogenase I (bidirectional) and hydrogenase II (uptake) of Clostridium pasteurianum (strain W5) have been determined on the basis of quantitative amino acid analyses. The iron and acid-labile sulfide values are approximately 20 and 18 atoms per molecule of hydrogenase I and 14 and 11 atoms per molecule of hydrogenase II, respectively. These amounts are substantially greater than previously reported values, which relied on protein concentration determined by colorimetric assay. The oxidized hydrogenases exhibit unusual EPR signals that originate from a novel type of iron-sulfur center, termed the hydrogenase or H cluster, which covalently binds the inhibitor CO. This EPR signal represents approximately one unpaired electron per molecule in each enzyme with and without bound CO, which is consistent with the presence of one oxidized H cluster (S = 1/2) per enzyme molecule. The two enzymes also contain ferredoxin-type four-iron centers or F clusters. The EPR signals from the F clusters observed in the reduced forms of hydrogenase I and hydrogenase II account for approximately four and one unpaired electron per molecule, respectively. We conclude from the iron determinations and the EPR results, together with a reevaluation of previous spectroscopic data, that in both hydrogenases the H cluster probably comprises six iron atoms. Mechanistic models of the two hydrogenases are presented that account for their cluster compositions and the dramatic differences in their catalytic activities.

Cross-linking of nitrogenase components. Structure and activity of the covalent complex

The nitrogenase complex from Azotobacter vinelandii is composed of the MoFe protein (Av1), an alpha 2 beta 2 tetramer, and the Fe protein (Av2), a gamma 2 dimer. During turnover of the enzyme, electrons are transferred from Av2 to Av1 in parallel with the hydrolysis of MgATP. Using the cross-linking reagent, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, we have identified some of the properties of the complex between the two components. The cross-linking reaction was highly specific yielding a single apparent Mr = 97,000 protein. The amount of cross-linked product was essentially independent of whether MgATP or MgADP were in the reaction. Also, the amount was maximum at high ratios of Av2 to Av1. The Mr = 97,000 protein was characterized by amino acid analysis and Edman degradation and was found to be consistent with a 1:1 complex of an Av2 gamma subunit and an Av1 beta subunit (the amino terminal serine subunit). The complex was no longer active in the nitrogenase reaction which supports, but does not prove, the requirement for dissociation of the complex after each electron transferred. Nitrogenase activity and cross-linking were inhibited in an identical way by NaCl, which suggests that electrostatic forces are critical to the formation of the electron transfer complex.

Kinetics of MgATP-dependent iron chelation from the Fe-protein of the Azotobacter vinelandii nitrogenase complex. Evidence for two states

Chelation of Fe from the Fe-protein component (Av2) of Azotobacter vinelandii nitrogenase has been investigated. The chelation, which requires MgATP binding by Av2, is best described as a two-exponential process. The rates for the two phases differed by approximately 10-fold and increased as the concentration of MgATP was increased. The rates for both phases were 50% of maximum at approximately 1.5 mM MgATP. At MgATP concentrations greater than 100 microM, the more rapid phase represented approximately 25% of the total Fe chelated from Av2. However, below 100 microM MgATP, the proportion of the faster phase decreased until at 20 microM MgATP, only a single phase could be detected. The properties of Av2 were studied at various stages of Fe chelation. The partially chelated protein was isolated from the reaction by gel filtration and was subjected to a second MgATP-dependent Fe chelation. Material isolated after the completion of the first phase regained biphasic kinetics in subsequent chelation reactions. However, if MgATP was present during the isolation of Av2, then only a single phase was observed in the subsequent chelation studies. In addition, the enzymatic activity of Av2 decreased concomitantly with total Fe chelation. To account for these observations, a model is presented in which Av2 exists in two conformers. Fe chelation is proposed to occur from either conformer but only when two MgATP are bound. Both conformers bind MgATP with the same affinity but are distinguished by a 10-fold difference in chelation rate. The two conformers are in equilibrium and can interconvert only in the absence of MgATP. That is, MgATP binding prevents the conversion of the two conformational states.

Purification, characterization and revised amino acid sequence of a second thioredoxin from Corynebacterium nephridii

A second thioredoxin, distinct from the one reported by Meng and Hogenkamp in 1981 (J. Biol. Chem. 256, 9174-9182), has been purified to homogeneity from an Escherichia coli strain containing a plasmid encoding a Corynebacterium nephridii thioredoxin. Thioredoxin genes from C. nephridii were cloned into the plasmid pUC13 and transformants were identified by complementation of a thioredoxin negative (trxA-) E. coli strain. The abilities of the transformants to support the growth of several phages suggested that more than one thioredoxin had been expressed [Lim et al. (1987) J. Biol. Chem. 262, 12114-12119]. In this paper we present the purification and characterization of one of these thioredoxins. The new thioredoxin from C. nephridii, designated thioredoxin C-2, is a heat-stable protein containing three cysteine residues/molecule. It serves as a substrate for C. nephridii thioredoxin reductase and E. coli and Lactobacillus leichmannii ribonucleotide reductases. Thioredoxin C-2 catalyzes the reduction of insulin disulfides by dithiothreitol or by NADPH and thioredoxin reductase and is a hydrogen donor for the methionine sulfoxide reductase of E. coli. Spinach malate dehydrogenase (NADP+) and phosphoribulokinase are activated by this thioredoxin while glyceraldehyde-3-phosphate dehydrogenase (NADP+) is not. Like the thioredoxin first isolated from C. nephridii, this new thioredoxin is not a reducing substrate for the C. nephridii ribonucleotide reductase. The complete primary sequence of this second thioredoxin has been determined. The amino acid sequence shows a high degree of similarity with other thioredoxins. Surprisingly, in contrast to the other sequences, this new thioredoxin contains the tetrapeptide -Cys-Ala-Pro-Cys- at the active site. With the exception of the T4 thioredoxin, this is the first example of a thioredoxin that does not have the sequence -Cys-Gly-Pro-Cys-. Our results suggest that, like plant cells, bacterial cells may utilize more than one thioredoxin.

Identification of the reactive sulfhydryl and sequences of cysteinyl-tryptic peptides from beef heart aconitase

In an accompanying paper (Kennedy, M. C., Spoto, G., Emptage, M. H., and Beinert, H. (1988) J. Biol. Chem. 263, 8190-8193), it was shown that one cysteine per mol of aconitase is modified by a variety of sulfhydryl reagents. We have identified the tryptic peptide that contains the iodoacetamide-reactive cysteine. We have also demonstrated that this cysteine is the primary site of modification by phenacyl bromide (2-bromoacetophenone), a spin label analogue of N-ethylmaleimide (HO-461) and iodoacetate in both the 3Fe and 4Fe forms of aconitase. The amino acid sequence of the peptide containing the reactive cysteine from beef heart aconitase shares no homology with the reactive cysteine-containing peptide reported for pig heart aconitase (Hahm, K.-S., Gawron, O., and Piszkiewicz, D. (1981) Biochim. Biophys. Acta 667, 457-461). We also report the amino acid compositions and sequences of seven other cysteine-containing tryptic peptides from beef heart aconitase. However, none of the cysteinyl peptides isolated were found to correspond to the reported pig heart reactive cysteinyl peptide. Evidence is also presented that no previously unreactive cysteine becomes exposed and reactive to sulfhydryl reagents in the conversion from the [4Fe-4S] cluster of the enzyme to the [3Fe-4S] cluster. We conclude from this that any potential cysteine ligand to the Fea site of the cluster must be inaccessible to solvent in the 3Fe form or, alternatively, that active 4Fe aconitase does not contain a cysteine ligand to the Fea site.