Overexpression in Escherichia coli and purification of the 6-phosphogluconate dehydrogenase of Trypanosoma brucei

The gene encoding 6-phosphogluconate dehydrogenase (EC 1.1.1.44) from Trypanosoma brucei was cloned into the overexpression vector pET3a which utilizes the T7 polymerase gene expression system. Up to 40% of total cell protein consisted of the trypanosome enzyme when expression was induced in Escherichia coli host strains at 28 degrees C. The enzyme was rapidly degraded at temperatures higher than 30 degrees C. The T. brucei enzyme was purified to near homogeneity (as judged by SDS-polyacrylamide gel electrophoresis) using a two-step purification method, involving a DE-52 cellulose batch preparation followed by 2' AMP-agarose affinity chromatography. The purified protein crystallized readily. A molecular model of the trypanosome enzyme based on its mammalian counterpart revealed differences between the two enzymes in residues involved in cofactor binding.

Bioequivalence of two methotrexate formulations in psoriatic and cancer patients

OBJECTIVE

To compare the bioequivalence of a generic methotrexate (MTX) tablet (Mylan) with that of a brand-name (Lederle) product.

DESIGN

A single-dose, randomized, crossover study.

SETTING

Clinical Research Center (CRC) at a university hospital.

PATIENTS

Men and women who had a diagnosis of malignancy or psoriasis who were at least 21 years old.

METHODOLOGY

Two overnight study periods were scheduled at the CRC at least one week, but not more than two weeks apart. Each period consisted of a 10-hour fast prior to and 4 hours following oral MTX 15 mg administered as six 2.5-mg tablets. Blood samples were collected over 48 hours. Plasma MTX concentrations were determined using an HPLC assay. Area under the curve from zero to infinity (AUC0-infinity) was calculated by the log-trapezoidal method.

RESULTS

Twenty-two patients (21 psoriasis, 1 colon cancer) aged 23-61 years completed both study periods. Mean values for peak concentration, time to peak concentration, and AUC0-infinity were 0.80 mumol/L, 1.2 hours, and 3.0 mumol.h/L, respectively, for Mylan's MTX tablets and 0.81 mumol/L, 1.4 hours, 3.0 mumol.h/L, respectively, for Lederle's MTX. Normalization for weight or body surface area did not affect interpatient variability. Relative bioavailability of generic MTX was 99.2 percent. Rate and extent of absorption were not significantly different and the confidence intervals were within the range of 80-120 percent required by the Food and Drug Administration.

CONCLUSIONS

Mylan's MTX tablet is bioequivalent to Lederle's product.

Preliminary crystallographic study of 6-phosphogluconate dehydrogenase from Trypanosoma brucei

We have obtained well-ordered single crystals of 6-phosphogluconate dehydrogenase, an enzyme of the oxidative branch of the pentose phosphate pathway, from Trypanosoma brucei. The crystals are trigonal rhombs with unit cell dimensions a = b = 135.1 A, c = 116.7 A and belong to one of the enantiomorphic pair of space groups P3(1)21/P3(2)21. X-ray diffraction to better than 2.8 A has been recorded using a rotating anode CuK alpha source. Elucidation of the three-dimensional structure of the T. brucei enzyme will, by indicating structural differences from the known sheep enzyme structure, aid the design of mutants to probe the active site. Knowledge of the structure will also assist in assessing the potential use of rationally designed compounds to inhibit this enzyme specifically.

Quiz: case report 776. Chondromyxoid fibroma of femur

CMF is a rare neoplasm of bone, comprising less than 1% of primary bone tumors. The neoplasm was first described in 1948 by Jaffe and Lichtenstein as a separate entity from chondrosarcomas, having slightly different plain film characteristics and a benign clinical course. As of 1985, Kreicbergs, Lonnquist, and Willems estimated that approximately 400 cases have been published. Recently, we encountered a CMF with an unusual clinical presentation. The efficacy of MRI studies is shown.

Sheep 6-phosphogluconate dehydrogenase. Revised protein sequence based upon the sequences of cDNA clones obtained with the polymerase chain reaction

Sheep liver 6-phosphogluconate dehydrogenase (6-PGDH) is an enzyme of the pentose phosphate pathway. Evidence has appeared which suggests that the 6-PGDH protein sequence determined previously by direct analysis of the protein isolated from ovine liver is incorrect. Determining the enzyme's DNA sequence was considered to be the best way of solving the problem. In the first instance, a degenerate forward and a degenerate reverse primer were designed on the basis of the known protein sequence, and a partial-length cDNA clone was isolated from total sheep liver cDNA using the polymerase chain reaction. The clone encoded the expected part of the protein sequence. The clone was unsuccessfully used as a prime-cut probe to screen a sheep liver library and a bovine heart library. As a result, the polymerase chain reaction was utilized again to successfully generate a family of overlapping cDNA clones encoding a mature protein of 482 amino acids. The mature protein sequence encoded by the cDNA differs significantly from the sequence derived by direct analysis of the protein, but on closer examination the fundamental difference is caused by the incorrect placement of three enzyme fragments obtained by cyanogen bromide cleavage during the direct sequence analysis of the protein. Placing the fragments in the correct order results in the two sequences being virtually identical except for some minor amino acid changes between the amide and acid forms, and a small number of deletions and insertions.

Community-based projects for the prevention of developmental disabilities

Community projects are a central feature of the Centers for Disease Control's (CDC's) Disabilities Prevention Program. Twenty-eight states now have such programs, and they use community projects to stimulate local involvement in disability prevention and as a setting to evaluate prevention needs and preventive interventions.

A two-step purification procedure for sheep liver 6-phosphogluconate dehydrogenase

A two-step procedure for the purification of 6-phosphogluconate dehydrogenase (EC 1.1.1.44; 6-PGDH) from sheep liver is described. The enzyme is directly bound to cellulose phosphate by batch extraction and eluted with a linear salt gradient. Purification is completed by affinity chromatography using NADP(+)-agarose. The result is 6-PGDH of high purity, greatly increased yield, and the highest specific activity yet achieved, with a significant reduction in the purification time.

The structure of 6-phosphogluconate dehydrogenase refined at 2.5 A resolution

The three-dimensional structure of ovine 6-phosphogluconate dehydrogenase, refined at 2.5 A resolution with a residual for all data of 18.5%, is reported. This model, based on improved diffraction data and a corrected sequence, supersedes that reported earlier. Each subunit of the dimer has three domains: a beta-alpha-beta domain binds NADP; an all alpha domain provides much of the dimer interface; the C-terminal tail burrows into the second subunit.

Nonlinear-optical absorption in InGaAs/InAlAs multiple quantum wells

We have measured the room-temperature intensity dependence of the optical transmission of an In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As multiple-quantum-well structure from 1.5 to 1.7 microm. The absorption is calculated from the transmission by taking into account the wavelength dependence of the reflection coefficients. An intensityof 15 kW cm(-2) is required to reduce the absorption by one half for excitation at the edge of the 1H-lC transition absorption band. For intensities exceeding 10(7) W cm(-2), complete saturation of the absorption is observed. A theoretical model is described that fits the intensity dependence of the absorption right upto saturation at two wavelengths and predicts a carrier lifetime of 0.75 nsec, which has been confirmed by independent measurements.

Barley yellow mosaic virus (BaYMV) and BaYMV-M: two different viruses

Serological and physical properties of isolated particles as well as reactions of barley cultivars after virus inoculation showed that the yellow disease of barley is caused by different viruses. Results summarized in this paper suggest that the European isolates BaYMV-So and BaYMV-NM are closely related to, or identical with, BaYMV-J first reported from Japan, whereas BaYMV-M differs in several properties. Therefore, it seems justified to describe BaYMV-M as a separate virus tentatively designated barley mild mosaic virus.

On the measurement of susceptibility in epidemiologic studies

Although relative effects of risk factors (relative risks) are commonly used in epidemiologic studies of disease, these measures do not provide estimates of the proportion of persons who are "susceptible" to the risk factor. Susceptibility may be defined under a simple sufficient cause model as the underlying factor (or set of factors) sufficient to make a person contract a disease following exposure. The authors derive simple estimates of the proportion of susceptibles in a population based on relative risk, and disease and exposure frequencies. The proportion of susceptibles increases with increasing disease frequency and relative risk but declines at high exposure frequency. For many chronic diseases with a lifetime risk in the range of 1-10 per cent, rare exposures suggest the presence of a large proportion of susceptibles, whereas common exposures suggest fewer susceptibles in the population. The estimation of the proportion of susceptibles is important in the search for genetic and environmental factors that interact with measured risk factors in etiologic studies of disease.

The use of attributable fraction in the design and interpretation of epidemiologic studies

Because of the etiologic heterogeneity present in many diseases and the interaction among causal factors in the development of disease, relative risks relating any one exposure to a disease may be low, especially in the presence of common exposures. Nevertheless, in the design of epidemiologic studies, arbitrary values of relative risks are often used to determine the sample size required to detect an association between a particular exposure and a disease outcome. Such an approach may not yield adequate statistical power to detect an association. In this commentary, the authors point out the value of using the attributable fraction to determine an appropriate value of relative risk to use for sample size calculations. The approach is particularly useful in cluster investigations where the magnitude of the expected attributable fraction can be readily estimated from the observed and expected rates of disease. Specification of an attributable fraction is also useful in the design of case-control studies of etiologically heterogeneous diseases, especially when common exposures are suspected. Finally, the relationship among attributable fraction, relative risk and exposure frequency is valuable in interpreting results of an epidemiologic study and gaining insight into the differences in relative risk estimates found in various studies.

The epidemiology and public health significance of Rett syndrome

Current data indicate that Rett syndrome is an important contributor to the total burden of idiopathic mental retardation. Studies from Sweden suggest that among girls the prevalence of Rett syndrome may be twice the prevalence of phenylketonuria. Successful epidemiologic studies of idiopathic mental retardation syndromes will require both large sample sizes and homogeneous populations. Because Rett syndrome is a relatively homogeneous and common syndrome of idiopathic mental retardation, epidemiologic methods may be more productive in the study of Rett syndrome than in other syndromes of mental retardation that are less clinically homogeneous. The approaches used in studying Rett syndrome epidemiologically may later be useful in the study of other syndromes of idiopathic mental retardation.

An epidemiologic approach to ecogenetics

Although "ecogenetics" seeks to examine genetically mediated differences in susceptibility to environmental agents, researchers often examine the relation between genetic markers and disease without regard to environmental determinants. By using epidemiologic definitions of genotype-environment interaction, it can be shown that the relative risk of disease for the genetic marker is a function of the frequency of exposure to the environmental agent, the strength of interaction between the genotype and the agent, and the specificity of the environmental effect vis-à-vis the genotype. Using examples from the literature, we illustrate under six patterns of genotype-environment interaction that the relative risk associated with the marker can fluctuate markedly. However, with infrequent exposures, the relative risk is close to unity (implying no genetic effect) even in the face of strong genotype-environment interaction. Alternatively, elevated relative risks imply a frequent environmental exposure or a strong pattern of interaction. We suggest that genetic marker-disease associations be evaluated within the context of an epidemiologic study design that considers specific environmental determinants of risk.

Sequence identity between a lysine-containing peptide from Leuconostoc mesenteroides glucose-6-phosphate dehydrogenase and an active site peptide from human erythrocyte glucose-6-phosphate dehydrogenase

Peptides recently isolated and sequenced from a bacterial (Leuconostoc mesenteroides) glucose-6-phosphate dehydrogenase are remarkably homologous to an active site region of the human erythrocyte enzyme, although the enzymes differ in their overall amino acid composition and kinetic properties. The computer program ALIGN, used to determine the best alignment between the two enzyme sequences, gives match-scores which are statistically highly significant.

Teaching generalization of purchasing skills across community settings to autistic youth using videotape modeling

Three young autistic adults were trained to purchase items. Training was conducted in one setting with concurrent generalization probes taken in three community stores. Training in one setting failed to produce generalization to the three probe settings. Generalization training, which consisted of viewing videotapes of models who purchased items in the probe settings and answering questions about the models' responses, was then introduced. Training with the videotapes resulted in generalization to the three community stores. Results of the use of videotapes as a cost-effective means to program generalization in community training programs are discussed.

Vietnam veterans' risks for fathering babies with birth defects

Vietnam veterans' risks for fathering babies with major structural birth defects were assessed using a case-control study. Information regarding military service in Vietnam was obtained from interviews with mothers and fathers of babies in case and control groups and from review of military records. Vietnam veterans, in general, did not have an increased risk of fathering babies with defects (all types combined; relative risk estimate, 0.97). Vietnam veterans who had greater estimated opportunities for Agent Orange exposure did not seem to be at greater risk for fathering babies with all types of defects combined. However, for a few specific types of defects the estimated risks were higher for subgroups of Vietnam veterans that may have had a greater likelihood of exposure to Agent Orange. These seemingly higher risks could be chance events, the result of some experience in the Vietnam service of the father, or the result of some other unidentified risk factor.

Trends in postneonatal mortality in the United States. 1962 through 1978

Trends in postneonatal mortality (PNM) rates in the United States were analyzed for the period 1962 through 1978 using National Center for Health Statistics birth and death certificate data. The PNM rates declined from 5.5 to 3.6 per 1,000 live births for whites and from 15.6 to 7.6 per 1,000 live births for blacks. Most of the decline in PNM rates could be accounted for by a drop in mortality from infectious diseases. A dramatic increase occurred in the reported rates of unexplained sudden infant death (SID), which emerged as the leading reported cause of PNM. The second leading cause of PNM was birth defects among whites and infectious diseases among blacks. Gaps in PNM continued to exist between whites and blacks, and between metropolitan and nonmetropolitan areas. These gaps suggest that further improvement in PNM may be possible by improving access to health care. The massive increase in the rates of SID, although partially explained by coding or reporting phenomena, warrants active pursuit for a better pathophysiologic and etiologic delineation of the entity.

Clinical interpretation of maternal serum alpha-fetoprotein concentrations

Concentrations of maternal serum alpha-fetoprotein provide the basis for decisions to proceed to ultrasonography and amniocentesis in the multistaged screening/diagnostic process used for the prenatal detection of open neural tube defects, abdominal wall defects, and twins. The concentration of maternal serum alpha-fetoprotein at or above which women should be advised that amniocentesis is available (cutoff levels for amniocentesis) varies, depending upon a number of factors, such as maternal weight, race, residence, and gestational age. We briefly describe a methodology for computing the predicted risks of fetal conditions associated with a given concentration of maternal serum alpha-fetoprotein adjusted for important variables. This adjustment methodology provides a straightforward means for clinical laboratories to report results of assays of maternal serum alpha-fetoprotein in terms of predicted risks, to facilitate understanding by the physician and patient of the clinical meaning of the results of maternal serum alpha-fetoprotein testing.

Crystallisation and preliminary X-ray data of ribulose-1,5-bisphosphate carboxylase from spinach

Crystals of a tertiary complex of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase with the activators Mg and CO(2) have been grown. These crystals diffract strongly to 1.6 A resolution. The spacegroup is C222(1) with unit cell dimensions a = 158.6 A, b = 158.6 A, c = 203.4 A. Additional local symmetry is apparent in the pattern of absences and the intensity distribution of the X-ray precession photographs. The photographs have been interpreted in terms of a molecule (consisting of eight large and eight small subunits, L(8)S(8)) with 222 symmetry and a molecular centre shifted 2 A in the x direction from the origin of the unit cell. The asymmetric unit contains half the L(8)S(8) molecule. The intensity distribution suggests that the molecular symmetry does not deviate far from 422. These crystals are compared with other crystalline forms of the enzyme and the implications of these results are discussed.