A meta-analytic inquiry into the relationship between selected risk factors and problem behavior

Identifying the predictors of problem behavior is essential both for understanding the causes of such behavior and for preventing it. Although a great deal of research has sought to identify the factors predictive of problem behavior, much of the research to date has been correlational and tells us little about causality. This study attempts to improve on the correlational research by applying meta-analytic techniques to existing experimental and quasi-experimental studies of school-based prevention. The following 3 risk factors were examined: academic performance, bonding to school, and social competency skills. The most convincing evidence of a relationship between risk and problem behavior was found for bonding to school. Positive changes in attachment and commitment to school resulting from the preventive interventions were consistently accompanied by positive changes in problem behavior. Preventive interventions that produced improvements in academic performance produced moderate improvements in problem behavior. With regard to social competence, the association depended in large part on the type of measure used to assess social competency skills. Changes in self-report measures of social competency were unrelated to changes in problem behavior, whereas a strong positive correlation was observed between changes in ratings and observations of social competency by others and improvements in problem behavior.

The role of method in treatment effectiveness research: evidence from meta-analysis

A synthesis of 319 meta-analyses of psychological, behavioral, and educational treatment research was conducted to assess the influence of study method on observed effect sizes relative to that of substantive features of the interventions. An index was used to estimate the proportion of effect size variance associated with various study features. Study methods accounted for nearly as much variability in study outcomes as characteristics of the interventions. Type of research design and operationalization of the dependent variable were the method features associated with the largest proportion of variance. The variance as a result of sampling error was about as large as that associated with the features of the interventions studied. These results underscore the difficulty of detecting treatment outcomes, the importance of cautiously interpreting findings from a single study, and the importance of meta-analysis in summarizing results across studies.

A selective inhibitor of Escherichia coli prephenate dehydratase

To identify selective prephenate dehydratase (PDT) inhibitors, a series of substituted biphenic acid derivatives was synthesized using the Ullmann reaction. Screening experiments identified 18 as a promising new PDT inhibitor.

The way in which intervention studies have "personality" and why it is important to meta-analysis

Intervention studies represent webs of interrelated substantive and methodological characteristics that take on different patterns in different studies and different intervention areas. All too often, meta-analysts do not give close attention to the possibility that these interrelated differences among studies are related in complex ways to study effect sizes and, consequently, run considerable risk of reporting results that are misleading or flatly wrong. To remedy this situation, improvements are needed in both the method and practice of meta-analysis so that greater attention can be given to effect size variation, the generalizability of study results, and the systematic multivariate relationships between study characteristics and the effect sizes reported in those studies.

Adrenocortical tumorigenesis in transgenic mice: the role of luteinizing hormone receptor and transcription factors GATA-4 and GATA-61

Transgenic (TG) mice, bearing the Simian Virus 40 T-antigen (Tag) under a 6-kb fragment of the murine inhibin alpha-subunit promoter (inhalpha), develop gonadal tumors of granulosa or Leydig cell origin with 100% penetrance by the age of 5-7 months. When these TG mice were gonadectomized prepubertally, between 21-25 days of life, adrenal gland tumors were observed in each mouse by the age of 5-7 months. No adrenal tumors were detected in any intact TG, gonadectomized or intact or control non-TG littermates. The adrenocortical tumors appeared to originate from the X-zone of the adrenal cortex. If functional gonadectomy was induced by GnRH antagonist treatment or by cross-breeding of the TG mice into hypogonadotropic hpg genetic background, neither gonadal nor adrenal tumorigenesis appeared. This prompted a hypothesis that adrenal tumor development in inhalpha/Tag TG mice is related to elevated gonadotropin secretion, which is the most obvious difference between the surgical and functional gonadectomy models. The adrenal tumors and a cell line (Calpha1) derived from them, was found to express luteinizing hormone receptor (LHR), but no FSHR, and hCG treatment stimulated their proliferation. No FSHR was found in the adrenal glands. On the basis of this it was suggested that expression of the potent oncogene T-antigen, allow LH in adrenocortical cells to function as a tumor promoter, and induction of high level functional LHR expression in adrenal tumors. Given the induction of expression and regulation of the GATA-4 and GATA-6 zinc finger family of transcription factors in the gonads by gonadotropins, it was in our interest to explore their expression in the adrenals. We utilized the inalpha/Tag TG mouse model and pathological human adrenal samples to explore the role of GATA-4 and GATA-6 in adrenocortical tumorigenesis. Abundant GATA-6 mRNA expression was found in normal control adrenal cortex during mouse development, whereas GATA-4 mRNA was undetectable. In striking contrast to this, GATA-6 was absent from murine adrenocortical tumors, while GATA-4 mRNA expression was dramatically upregulated in the murine adrenal tumors as well as in human adrenocortical carcinomas. Taken together, these results suggest different roles for GATA-4 and GATA-6 in the adrenal gland, and implicate GATA-4 in adrenal LHR expression and tumorigenesis. Immunohistochemical detection of GATA-4 may serve as a useful marker in differential diagnosis of human adrenal tumors. In addition, the inhalpha/Tag TG model will be helpful for exploring the molecular mechanisms underlying adrenocortical tumorigenesis, ectopic LHR expression in adrenals and the GATA-4/LHR interaction that is related to adrenal tumorigenesis in TG mice.

Bioaccumulation of mercury from wastewater by genetically engineered Escherichia coli

Genetically engineered E. coli, which express both a Hg2+ transport system and metallothionein, were tested for their ability to remove mercury from wastewater. The wastewater contained more than ten different ions, including 2.58 mg/l mercury, and its pH was 9.6. Mercury uptake was faster from the wastewater than from distilled water, probably because of the higher ionic strength, as the high pH had little effect on mercury accumulation. EDTA also stimulated mercury uptake rather than inhibiting it. A hollow-fiber bioreactor was used to retain induced cells for continuous mercury uptake. The cells removed more than 99% of the mercury in the wastewater and the final amount of mercury accumulated was 26.8 mg/g cell dry weight, while none of the other ions were removed from the water. These results indicated that the induced cells had a high affinity and specificity for mercury.

Cloning and biochemical characterization of BglC, a beta-glucosidase from the cellulolytic actinomycete Thermobifida fusca

An operon, bglABC, that encodes two sugar permeases and a beta-glucosidase was cloned from a cellulolytic actinomycete, Thermobifida fusca, into Escherichia coli and sequenced. The bglC gene encoding an intracellular beta-glucosidase (beta-d-glucoside glucohydrolase, EC 3.2.1.21) belonging to glycosyl hydrolase family 1 was subcloned and expressed in E. coli. The purified enzyme (MW 53,407 Da; pI 4.69) hydrolyzed substrates containing both beta 1 --> 4 and beta 1 --> 2 glycosidic bonds, and was most active against cellobiose (Vmax = 29, Km = 0.34 mm), cellotriose, cellotetraose, and sophorose. The enzyme also showed aryl-beta-glucosidase activity on p-nitrophenyl-beta-d-glucopyranoside and p-nitrophenyl-beta-d-cellobioside. BglC had a pH optimum of 7.0 and a temperature optimum of 50 degrees C. The enzyme was stable at 60 degrees C, but was rapidly inactivated at 65 degrees C. BglC was inhibited by low concentrations of gluconolactone, but was insensitive to end-product inhibition by glucose and was not affected by Ca or Mg ions or EDTA. Its properties are well suited for use in a process to hydrolyze biomass cellulose to glucose.

Identification of MHC class II-restricted peptide ligands, including a glutamic acid decarboxylase 65 sequence, that stimulate diabetogenic T cells from transgenic BDC2.5 nonobese diabetic mice

Nonobese diabetic (NOD) mice spontaneously develop insulitis and destruction of pancreatic islet beta cells similar to type 1 diabetes mellitis in humans. Insulitis also occurs in the BDC2.5 TCR transgenic line of NOD mice that express the rearranged TCR alpha- and beta-chain genes of a diabetogenic NOD CD4 T cell clone. When activated with syngeneic islet cells in culture, BDC2.5 T cells adoptively transfer disease to NOD recipients, but the identity of the islet cell Ag responsible for pathogenicity is not known. To characterize the autoantigen(s) involved, BDC2.5 T cells were used to screen a combinatorial peptide library arranged in a positional scanning format. We identified more than 100 decapeptides that stimulate these T cells at nanomolar concentrations; they are then capable of transferring disease to NOD-scid mice. Surprisingly, some of the peptides include sequences similar (8 of 10 residues) to those found within the 528-539 fragment of glutamic acid decarboxylase 65. Although this 12-mer glutamic acid decarboxylase 65 fragment is only slightly stimulatory for BDC2.5 T cells (EC(50) > 100 microM), a larger 16-mer fragment, 526-541, shows activity in the low micromolar range (EC(50) = 2.3 microM). Finally, T cells from prediabetic NOD mice respond spontaneously to these peptide analogs in culture; this finding validates them as being related to a critical autoantigen involved in the etiology of spontaneous diabetes and indicates that their further characterization is important for a better understanding of underlying disease mechanisms.

Use of remifentanil in a patient with peripartum cardiomyopathy requiring Caesarean section

We describe a case of a 26 yr old primigravida at 39 weeks' gestation, with a diagnosis of peripartum cardiomyopathy, requiring urgent Caesarean section. The patient presented in severe heart failure and active labour. A general anaesthetic, using a target-controlled infusion of propofol and an intravenous infusion of remifentanil, was used to provide stable anaesthesia and analgesia for a successful delivery. The unusual diagnosis of peripartum cardiomyopathy and the potential benefits of the use of remifentanil in high-risk obstetric surgery are discussed.

Construction and characterization of an Escherichia coli strain genetically engineered for Ni(II) bioaccumulation

An Escherichia coli strain that accumulated Ni(II) was constructed by introducing the nixA gene (coding for a nickel transport system) from Helicobacter pylori into JM109 cells that expressed a glutathione S-transferase-pea metallothionein fusion protein. The resulting strain accumulated 15 micromol of Ni(II) per g (dry weight) from a 10 microM Ni(II) solution, four times the level taken up by JM109 cells. Ni(II) accumulation did not require an energy source, was inhibited by only 50% by 0.1 M NaCl, and occurred over the pH range from 3 to 9.

Meta-analyses in alcohol and other drug abuse treatment research

Meta-analysis is a quantitative method of synthesizing empirical evidence across a collection of related studies and addresses many of the weaknesses of traditional narrative forms of reviewing. This paper describes the basic methods for conducting a state-of-the-art meta-analysis and criticizes 11 extant meta-analyses of alcohol and other drug abuse treatment programs. Eight of these 11 meta-analyses used questionable methods and contributed little to our understanding of the effects of these programs. The paper concludes with a proposal for an archive of alcohol and other drug services research to facilitate and improve the quality of future meta-analyses.

A randomized, crossover comparison of warfarin products in the treatment of chronic atrial fibrillation

OBJECTIVE

To compare the dosing requirements and international normalized ratios (INRs) associated with two bioequivalent crystalline warfarin sodium products in patients with chronic atrial fibrillation.

METHODS

A multicenter, single-blind (prescriber), randomized, crossover evaluation of Apothecon warfarin and DuPont warfarin (Coumadin) was conducted in consenting adults with chronic or paroxysmal atrial fibrillation who had been receiving DuPont warfarin chronically for the prevention of thromboembolism. Patients were randomly assigned to initially either continue DuPont warfarin or receive Apothecon warfarin for four weeks, with weekly evaluation of dosage and INR changes, safety, and efficacy. Subsequently, patients crossed over and received the other product for four weeks.

RESULTS

There were 113 patients randomized to receive study treatment. Neither the propensity for a dosage change or an INR change nor the magnitude of a dosage change or INR change appeared related to a particular warfarin product (NS for each variable after each study period). After four weeks of treatment, the same number of patients (n = 7) experienced a > or = 20% change in warfarin dosage from the respective baseline with each product. The number of patients with INRs outside the desired protocol range after four weeks of treatment was similar for both groups (< 1.8, n = 9 for both products, or > 3.2, n = 9 for DuPont, n = 10 for Apothecon). No major hemorrhagic or thromboemoblic events occurred.

CONCLUSIONS

The results of this study show that Apothecon warfarin and DuPont warfarin provide equivalent anticoagulation in patients with chronic or paroxysmal atrial fibrillation.

Transcription factors GATA-4 and GATA-6 and a GATA family cofactor, FOG-2, are expressed in human ovary and sex cord-derived ovarian tumors

Previous studies have implicated transcription factors GATA-4 and GATA-6 in the regulation of murine ovarian development and function. In rodents, GATA-4 is expressed in granulosa cells of primary and early antral follicles, whereas GATA-6 is expressed in granulosa cells of late antral follicles and luteal glands. Both transcription factors can be detected in lesser amounts in theca cells and interstitial cells. We have now examined the expression of GATA-4 and GATA-6 in human ovaries, human granulosa-luteal (GL) cells and sex cord-derived tumors. We show by in situ hybridization and immunohistochemistry that GATA-4 and GATA-6 messenger RNA (mRNA) and GATA-4 protein are present in granulosa and theca cells in both preantral and antral follicles. Both human ovarian tissue samples and freshly isolated GL cells derived from preovulatory follicles of gonadotropin-treated women express GATA-4, GATA-6, and FOG-2 transcripts, and GATA-6 mRNA expression in GL cell cultures is stimulated by human CG and 8-bromo-cAMP. The vast majority of granulosa and theca cell tumors examined expressed GATA-4 and GATA-6. We also found that mRNA for FOG-2, a recently discovered regulator of GATA-4, is coexpressed with GATA-4 in human ovary samples, normal granulosa cells, and in sex cord-derived tumors. Our results demonstrate that GATA-4, GATA-6, and FOG-2 are expressed in human ovary and in granulosa and theca cell tumors. Our findings support a role for GATA-binding proteins in human ovarian folliculogenesis. Moreover, these data suggest that GATA factors may contribute to the phenotypes of sex cord-derived ovarian tumors.

Cloning, expression and characterization of a family 48 exocellulase, Cel48A, from Thermobifida fusca

The gene for a 104-kDa exocellulase, Cel48A, formerly E6, was cloned from Thermobifida fusca into Escherichia coli and Streptomyces lividans. The DNA sequence revealed a type II cellulose-binding domain at the N-terminus, followed by a FNIII-like domain and ending with a glycosyl hydrolase Family 48 catalytic domain. The enzyme and catalytic domain alone were each expressed in and purified from S. lividans and had very low catalytic activity on swollen cellulose, carboxymethyl cellulose, bacterial microcrystalline cellulose and filter paper. However, in synergistic assays on filter paper, the addition of Cel48A to a balanced mixture of T. fusca endocellulase and exocellulase increased the specific activity from 7.9 to 11.7 micromol cellobiose.min-1.mL-1, more than 15-fold higher than any single enzyme alone. Cel48A retained > 50% of its maximum activity from pH 5 to 9 and from 40 to 60 degrees C. Using SWISSMODEL, the amino-acid sequence of the Cel48Acd was modeled to the known structure of Clostridium cellulolyticum CelF. Family 48 enzymes are remarkably homologous at 35% identity for all their catalytic domains and some of the properties of the 10 members are discussed.

Prevention education and evaluation in U.S. medical schools: a status report

The Prevention Curriculum Assistance Program (PCAP) was initiated to help U.S. medical schools examine the extent to which they are evaluating the learning of medical students about disease prevention/health promotion. A survey was sent to all 144 allopathic and osteopathic medical schools, with an overall response rate of 68%. The results revealed more emphasis on teaching and evaluating the learning of medical students in the areas of clinical preventive services and quantitative methods, and less emphasis on the community dimensions of medical practice and health services organization and delivery. Written tests and unstructured observation are the most common methods of evaluation. Fewer than half of all respondents were satisfied with the quality of their assessment of student achievement in any of the four domains of prevention education. More than 30% expressed a desire to receive assistance with designing curricula and/ or evaluation methods in each of the four content areas examined. Several indicated their willingness to assist colleagues who want to improve their prevention curricula and/or measurement strategies. This study identified a need for more attention and support for prevention education and evaluation programs. Curriculum leaders can help by designating prevention a priority area and appointing faculty to be responsible for monitoring the content and quality of prevention teaching throughout the curriculum. Resources such as the Internet can be utilized to establish a network whereby medical schools can collaborate to improve their educational programs and evaluation methods in prevention.

Site-directed mutation of noncatalytic residues of Thermobifida fusca exocellulase Cel6B

Fifteen mutant genes in six loop residues and eight mutant genes in five conserved noncatalytic active site residues of Thermobifida fusca Cel6B were constructed, cloned and expressed in Escherichia coli or Streptomyces lividans. The mutant enzymes were assayed for catalytic activity on carboxymethyl cellulose (CMC), swollen cellulose (SC), filter paper (FP), and bacterial microcrystalline cellulose (BMCC) as well as cellotetraose, cellopentaose, and 2, 4-dinitrophenyl-beta-D-cellobioside. They were also assayed for ligand binding, enzyme processivity, thermostability, and cellobiose feedback inhibition. Two double Cys mutations that formed disulfide bonds across two tunnel forming loops were found to significantly weaken binding to ligands, lower all activities, and processivity, demonstrating that the movement of these loops is important but not essential for Cel6B function. Two single mutant enzymes, G234S and G284P, had higher activity on SC and FP, and the double mutant enzyme had threefold and twofold higher activity on these substrates, respectively. However, synergism with endocellulase T. fusca Cel5A was not increased with these mutant enzymes. All mutant enzymes with lower activity on filter paper, BMCC, and SC had lower processivity. This trend was not true for CMC, suggesting that processivity in Cel6B is a key factor in the hydrolysis of insoluble and crystalline cellulose. Three mutations (E495D, H326A and W329C) located near putative glycosyl substrate subsites -2, +1 and +2, were found to significantly increase resistance to cellobiose feedback inhibition. Both the A229V and L230C mutations specifically decreased activity on BMCC, suggesting that BMCC hydrolysis has a different rate limiting step than the other substrates. Most of the mutant enzymes had reduced thermostability although Cel6B G234S maintained wild-type thermostability. The properties of the different mutant enzymes provide insight into the catalytic mechanism of Cel6B.

Probing the catalytic mechanism of prephenate dehydratase by site-directed mutagenesis of the Escherichia coli P-protein dehydratase domain

The Escherichia coli bifunctional P-protein, which plays a central role in L-phenylalanine (Phe) biosynthesis, contains distinct chorismate mutase (CM) and prephenate dehydratase (PDT) domains as well as a regulatory (R) domain for feedback control by Phe. To elucidate the catalytic mechanism of PDT in the P-protein, 24 mutations of 15 conserved residues in the PDT domain were created, expressed in the pheA(-)E. coli strain NK6024, and studied for their effect on PDT activity. Fourteen mutant enzymes were purified to homogeneity, tested for feedback inhibition by Phe, and characterized by kinetic analysis and circular dichroism spectroscopy. Selected mutant enzymes were further studied by gel filtration, fluorescence emission, and microcalorimetry. In addition, a monofunctional PDT domain (PDT20, residues 101-285) was cloned and overexpressed in plasmid pET with expression levels up to 200-250 mg/L. PDT20 retained full PDT activity, lacked CM activity, and was insensitive to feedback inhibition by Phe. Four residues (T278, N160, Q215, and S208) were shown to be important for PDT catalysis. The values of k(cat)/K(m) for the S208A/C and T278S mutant enzymes were 100-fold lower, and 500-fold lower for the N160A and Q215A mutant enzymes than the wild-type (WT) protein. The T278A and T278V mutant enzymes displayed no measurable catalytic activity, yet bound both prephenate and a competitive inhibitor (S-DNBA) comparably to the WT protein. These data, taken together with the normal CD spectra of the mutant enzymes, strongly suggested that T278 was involved in the catalytic mechanism. To establish whether acidic residues were involved in catalysis, all the conserved Glu and Asp residues in the PDT domain were mutated to Ala. None of these mutations significantly reduced PDT activity, indicating that the acidic residues of the PDT domain are not directly involved in catalysis. However, two mutant enzymes (E159A and E232A) displayed higher levels of PDT activity (2.2- and 3.5-fold, respectively), which was due to enhanced substrate binding. For the double mutant enzyme (E159A-E232A), k(cat)/K(m) was ca. 7-fold higher than for the WT enzyme, while its K(m) was 4.6-fold lower.

Faculty perspectives of health promotion in allied health curricula: results of a national survey

More knowledge and skills related to health promotion/disease prevention are being required of health professionals. Allied health graduates entering the workforce will need academic preparation in these areas. This study assessed faculty perspectives on the status of health promotion content in allied health programs by a survey of 524 program directors. A questionnaire gathered information about perception of importance, level of representation, and method of delivery of health promotion content. Response rate was 41%. The majority of participants thought this content area was important for their programs and was highly or moderately represented in their curricula. Level of representation was significantly associated with requirement for accreditation. Programs in the Northeast were more likely to think health promotion was important and those in the West were more likely to have it integrated into their curricula. The most common delivery modality was guest lecture. Allied health is adopting health promotion curricular content, but further study is needed to assess programs and faculty expertise and identify strategies to ensure greater consistency of delivering material.

Effects of noncatalytic residue mutations on substrate specificity and ligand binding of Thermobifida fusca endocellulase cel6A

The availability of a high-resolution structure of the Thermobifida fusca endocellulase Cel6A catalytic domain makes this enzyme ideal for structure-based efforts to engineer cellulases with high activity on native cellulose. In order to determine the role of conserved, noncatalytic residues in cellulose hydrolysis, 14 mutations of six conserved residues in or near the Cel6A active-site cleft were studied for their effects on catalytic activity, substrate specificity, processivity and ligand-binding affinity. Eleven mutations were generated by site-directed mutagenesis using PCR, while three were from previous studies. All the CD spectra of the mutant enzymes were indistinguishable from that of Cel6A indicating that the mutations did not dramatically change protein conformation. Seven mutations in four residues (H159, R237, K259 and E263) increased activity on carboxymethyl cellulose (CM-cellulose), with K259H (in glucosyl subsite -2) creating the highest activity (370%). Interestingly, the other mutations in these residues reduced CM-cellulose activity. Only the K259H enzyme retained more activity on acid-swollen cellulose than on filter paper, suggesting that this mutation affected the rate-limiting step in crystalline cellulose hydrolysis. All the mutations lowered activity on cellotriose and cellotetraose, but two mutations, both in subsite +1 (H159S and N190A), had higher kcat/Km values (6.6-fold and 5.0-fold, respectively) than Cel6A on 2,4-dinitrophenyl-beta-D-cellobioside. Measurement of enzyme : ligand dissociation constants for three methylumbelliferyl oligosaccharides and cellotriose showed that all mutant enzymes bound these ligands either to the same extent as or more weakly than Cel6A. These results show that conserved noncatalytic residues can profoundly affect Cel6A activity and specificity.

A celR mutation affecting transcription of cellulase genes in Thermobifida fusca

Biosynthesis of extracellular cellulases in the cellulose-degrading actinomycete Thermobifida fusca is controlled by a transcriptional regulator, CelR, and cellobiose, which acts as an inducer interfering with the CelR-DNA interaction. We report the identification and characterization of a mutation in the celR gene that changes Ala(55) in the hinge helix of CelR to Thr. The wild-type and mutant celR genes were cloned in Escherichia coli, and their protein products were characterized. The CelR mutant protein bound DNA more weakly than the wild-type protein and formed a less stable complex with DNA in the presence of cellobiose. The results of Western analysis and gel retardation experiments suggest that CelR is produced constitutively and its DNA-binding activity is regulated through posttranslational modification.

Immunogenicity. I. Use of peptide libraries to identify epitopes that activate clonotypic CD4+ T cells and induce T cell responses to native peptide ligands

Recent studies have demonstrated the utility of synthetic combinatorial libraries for the rapid identification of peptide ligands that stimulate clonotypic populations of T cells. Here we screen a decapeptide combinatorial library arranged in a positional scanning format with two different clonotypic populations of CD4+ T cells to identify peptide epitopes that stimulate proliferative responses by these T cells in vitro. An extensive collection of mimic peptide sequences was synthesized and used to explore the fine specificity of TCR/peptide/MHC interactions. We also demonstrate that many of these deduced ligands are not only effective immunogens in vivo, but are capable of inducing T cell responses to the original native ligands used to generate the clones. These results have significant implications for considerations of T cell specificity and the design of peptide vaccines for infectious disease and cancer using clinically relevant T cell clones of unknown specificity.

Substrate heterogeneity causes the nonlinear kinetics of insoluble cellulose hydrolysis

Nonlinear kinetics are commonly observed in the enzymatic hydrolysis of cellulose. This nonlinearity could be explained by any or all of the following three factors: enzyme inactivation, product inhibition, or substrate heterogeneity. In this study, four different approaches were applied to test the above hypotheses using two Thermomonospora fusca endocellulases, E2 and E5. The lack of stimulation of cellulase activity by beta-glucosidase rules out the possibility of product inhibition as a cause of the observed nonlinearity. The results from the other three approaches all provide strong evidence against enzyme inactivation and strong evidence for substrate heterogeneity as the cause of the nonlinear kinetics. The most direct evidence for substrate heterogeneity is that pretreatment of swollen cellulose with either E2cd or E5cd gave a product that was hydrolyzed at a much (3- to 4-fold) slower rate than untreated swollen cellulose even though the initial treatment degraded only 15-18% of the substrate. Furthermore, the activation energy of E2 catalyzed hydrolysis of swollen cellulose increased from 10 kcal/mol for the initial rate to 29 kcal/mol for hydrolysis after 24% digestion.

Regulatory T cells in experimental allergic encephalomyelitis. II. T cells functionally antagonistic to encephalitogenic MBP-specific T cells show persistent expression of fasL

Naive LEW rats and animals that have recovered from active or adoptive EAE contain a subset of T cells that inhibit EAE in secondary recipients and are lytic for MBP-reactive T cell lines in culture. Here we explore various features of these regulatory T cell populations (RTC) with respect to (1) their frequency in animals following immunization with syngeneic MBP-reactive cell lines, (2) their ability to inhibit proliferative responses by MBP-reactive cell lines in culture, (3) their ability to lyse MBP-specific target cells, and especially (4) their prolonged expression of high levels of FasL following activation in culture correlating with their lytic effects on A20, a FasL-sensitive mouse lymphoma cell line. Inhibition studies indicate that mAbs specific for MHC class I and MHC class II molecules inhibit lysis of syngeneic MBP-reactive target T cells, soluble Fas protein shows some inhibition, but none of these agents inhibits the lytic effects of activated RTC on the A20 cell line.

Characterization of cadmium uptake in Lactobacillus plantarum and isolation of cadmium and manganese uptake mutants

Two different Cd(2+) uptake systems were identified in Lactobacillus plantarum. One is a high-affinity, high-velocity Mn(2+) uptake system which also takes up Cd(2+) and is induced by Mn(2+) starvation. The calculated K(m) and V(max) are 0.26 microM and 3.6 micromol g of dry cell(-1) min(-1), respectively. Unlike Mn(2+) uptake, which is facilitated by citrate and related tricarboxylic acids, Cd(2+) uptake is weakly inhibited by citrate. Cd(2+) and Mn(2+) are competitive inhibitors of each other, and the affinity of the system for Cd(2+) is higher than that for Mn(2+). The other Cd(2+) uptake system is expressed in Mn(2+)-sufficient cells, and no K(m) can be calculated for it because uptake is nonsaturable. Mn(2+) does not compete for transport through this system, nor does any other tested cation, i.e., Zn(2+), Cu(2+), Co(2+), Mg(2+), Ca(2+), Fe(2+), or Ni(2+). Both systems require energy, since uncouplers completely inhibit their activities. Two Mn(2+)-dependent L. plantarum mutants were isolated by chemical mutagenesis and ampicillin enrichment. They required more than 5,000 times as much Mn(2+) for growth as the parental strain. Mn(2+) starvation-induced Cd(2+) uptake in both mutants was less than 5% the wild-type rate. The low level of long-term Mn(2+) or Cd(2+) accumulation by the mutant strains also shows that the mutations eliminate the high-affinity Mn(2+) and Cd(2+) uptake system.