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E A Williams

Publications and source records attributed to E A Williams.

18 recordsLinked to original sources
PubMed1992

Human dihydrofolate reductase: reduction of alternative substrates, pH effects, and inhibition by deazafolates.

The kinetics of the NADPH-dependent reduction of 7,8-dihydrofolate, folate, and 7,8-dihydrobiopterin by human dihydrofolate reductase have been examined over the pH range from 4.0 to 9.5. The V and V/K profiles obtained with the three substrates indicate that a single ionizing residue at the active site of the enzyme must be protonated for catalysis. Both the maximum velocity of the reactions and the rate of interaction of the substrates with the enzyme-NADPH complex decrease in the order dihydrofolate greater than dihydrobiopterin much greater than folate. From the pK values of the V/K profiles, it can be concluded that, while dihydrofolate behaves as a sticky substrate and dihydrobiopterin exhibits slight stickiness, folate is not a sticky substrate. Further support for this conclusion comes from the results of deuterium isotope effects. The pK values obtained from both the V and V/Kfolate profiles are similar to the intrinsic pK value of 5.6 for both the free enzyme and the enzyme-NADPH complex. The folate analogue, 5-deazafolate, is not a substrate, but it undergoes strong interaction with the enzyme. This interaction, which is enhanced by the presence of NADPH, is due to protonation of the bound ligand that does not involve the single ionizing group at the active center of the enzyme. Difference spectra yield evidence for the protonation of bound 5-deazafolate and show that, on binding to the enzyme-NADPH complex, the pK of the N-8 atom is raised to about 10 from a value of about 4 in solution. The results are in accord with those of a recent paper on the three-dimensional structure of the enzyme-5-deazafolate complex [Davies, J.F., Delcamp, T.J., Prendergast, N.J., Ashfors, V.A., Freisheim, J.H., & Kraut, J. (1990) Biochemistry 29, 9467-9479] which indicate that there is hydrogen bond formation between N-8 of the ligand and the carbonyl group of Ile-7. However, the present findings do not support the idea that bound 5-deazafolate resembles the transition-state complex for folate reduction. Quinazolines also interact strongly with the enzyme but in a pH-independent manner. The dissociation constants for the binary complexes are an order of magnitude lower than that for the binding to the enzyme of unprotonated 5-deazafolate. This difference reflects the hydrophobic nature of the amino acid residues at the active site that are near the N-5 and N-8 nitrogens of bound pterins.

Folic Acid↗
PubMed1992

Cocaine, social behavior, and alcohol-solution drinking in monkeys.

Eight group-living male monkeys received cocaine (0 to 3.0 mg/kg) individually or as a group. Cocaine suppressed social affiliative behaviors, eating, and drinking (of both alcohol and control solutions). It induced bizarre stereotypies, hypervigilance, panic-like fleeing, enhancement and then suppression of locomotion, and a seizure. Cocaine had little effect on aggressiveness or sexual behavior. Proportion of time spent lying or sitting changed significantly. Cocaine produced severe behavioral abnormality in this social setting.

Agonistic Behavior↗
PubMed1991

Characterization of tightly bound substrates in pure preparations of dihydrofolate reductase: implications for studies on enzymes.

Investigations have been made to determine the identity and binding characteristics of the pterins that are bound tightly to dihydrofolate reductases which are isolated from vertebrate sources by a well established procedure. This procedure involves the binding of enzyme to a Sepharose-methotrexate column, elution with dihydrofolate and removal of free dihydrofolate by dialysis or by size-exclusion chromatography. Addition to such preparations of NADPH results in oxidation of the nucleotide and from the progress curves so obtained, it is possible to identify the bound pterin and to calculate the stoichiometry of binding. The data indicated that stoichiometric amounts of dihydrofolate or folate plus dihydrofolate were bound to the dihydrofolate reductases. It can also be concluded that binding occurs at the active sites of the enzymes. Enzyme preparations from which bound pterin had been removed by isoelectric focussing reacted with folate or dihydrofolate to form 1:1 enzyme-pterin complexes from which the pterin could not be removed by dialysis or by size-exclusion chromatography. From the magnitude of the dissociation constants for the enzyme-pterin complexes and the concentration of enzyme present in fractions after the step involving affinity chromatography on Sepharose-methotrexate, it could be concluded that the presence of bound folate and/or dihydrofolate in pure preparations of dihydrofolate reductase is simply a consequence of an association-dissociation reaction. Preparations of the enzyme from bacterial sources were also found to contain bound pterins. The findings have implications with respect to kinetic and thermodynamic studies on dihydrofolate reductase and other enzymes which are isolated by affinity chromatography techniques.

Chromatography↗
PubMed1991

Medical and social outcome in adolescents with end-stage renal failure.

Clinical information was collected on 118 adolescents who developed ESRF at age 143 months or older and were treated between 1966 and 1986 at the Toronto Hospital for Sick Children. The cumulative survival rate in transplanted patients (N = 109) was 80.1% after 15 years. Survival rates after four years were 93.9% in transplanted and 46.9% in nontransplanted patients (P less than 0.001). No patient receiving dialysis alone (N = 9) was followed longer than four years. Nine patients received three transplants and had an 89% survival rate. Six of these had a functioning graft at end of the follow-up. The cumulative survival of the entire group was 76.4% at eighteen years. Forty-two (35.6%) patients had a height below the third percentile. Functional status obtained by a structure telephone interview with a member of the present treating nephrology service was good (G) or excellent (E) for 66.7% of all patients (73.5% of transplant patients (N = 68) and 45% of dialysis patients (N = 20). Hemodialysis patients functioned less well [25% G/E (N = 12)] than peritoneal dialysis patients [75% G/E (N = 8)]. Most patients achieved an appropriate level of formal education although more slowly than normal adolescents. Only 11 patients were neither enrolled in an educational institution nor employed. We conclude that aggressive treatment for adolescents with ESRF is an appropriate application of health care resources.

Adolescent↗
PubMed1990

Initiating ethanol drinking in a simian social group in a naturalistic setting.

We examined in nine group-living, male Japanese Snow monkeys the initiation of alcohol-drinking behavior in an enriched environment where both social and nonsocial stimuli could influence drinking. The monkeys usually could move freely between an indoor shelter and a large outdoor corral, which contained three drinkometers. During daily 2-hr sessions in pre- and post-training periods (with food and water available ad libitum), the drinkometers held (on different days) Koolaid-saccharin, water, water with 5% ethanol, Koolaid-saccharin with 5% ethanol, or Koolaid-sucrose with acetic acid (matched in calories and palatability to Koolaid-saccharin with 5% ethanol). Between pre- and post-training periods was a long training period, in which Koolaid-saccharin with various ethanol concentrations was presented with the daily food ration in 2-hr drinking sessions. On other selected training days, water with 5% ethanol was presented. During training sessions some monkeys drank high doses; others did not. During the period of peak drinking, the daily mean ethanol consumption ranged among animals from 0.54-1.99 ml/kg. Blood ethanol concentrations then sometimes exceeded 100 mg/dl. During the post-training period, with return to ad libitum food and water, consumption declined from these peaks, but remained significantly higher than pretraining consumption; the ethanol solution was established as a reinforcer. Monkeys differed significantly in the extent of this pre/post increase. In both pre- and post-training periods, consumption was significantly greater when all three drinkometers operated, compared with only one. On pretraining days when only one drinkometer operated, more dominant animals drank significantly more than less dominant animals; this difference disappeared by the post-training period, as less dominant animals learned to use the drinkometers at times when the dominant animals eschewed the machines. Pretraining consumption did not predict (among animals) post-training consumption. Before, during, and after training, these animals drank less of both alcohol and control solutions than did members of another species, which we had studied in smaller indoor pens. We discuss possible explanations and implications.

Alcohol Drinking↗
PubMed1979

Late failure of the Manchester prosthesis. Its relationship to the disease process.

The results of thirty-one Manchester knee arthroplasties performed on twenty-eight patients are reviewed. There were sixteen patients with rheumatoid arthritis all of whom were satisfactory at the time of follow-up. Of the fifteen patients with osteoarthritis over half the arthroplasties failed after between twelve and thirty-six months. We suggest that resurfacing arthroplasty of the knee using the Manchester prosthesis should be used only for rheumatoid patients.

Adult↗
PubMed1978

T cell-specific activity in rabbit anti-human thymocyte globulin. Correlation with immunosuppresive activity in nonhuman primates.

Spotaneous E rosette-forming (T) lymphocytes were monitored in the peripheral blood of rhesus monkeys receiving a 5-day course of rabbit anti-human thymocyte globulin (RATG) after skin allotransplantation. Mean graft survival in RATG-treated recipients was 32.3 +/- 7.6 (SD) days compared with 8.2 +/- 1.7 (SD) days in controls. The percentage and total number of circulating T cells fell precipitously after RATG treatment and recovered slowly. Linear regression analysis showed that the recovery pattern of the total number of circulating T cells, but not the percentage of T cells, was significantly correlated with rejection. Specific antihuman T cell antibody was detected in RATG preparations after extensive absorption with human erythrocytes, platelets, and B lymphoblastoid cells. The cytotoxic titers of B cell-absorbed RATG preparations to human peripheral blood lymphocytes showed a significant correlation with the mean skin allograft survival times obtained in RATG-treated primates. Overall the data suggest that the immunosuppressive potency of RATG in the primate skin graft assay is related in large part to its anti-T cell activity.

Animals↗
PubMed1976

Uterovaginal agenesis.

Experience in the diagnosis and treatment of certain developmental anomalies of the reproductive tract is described, with particular reference to uterovaginal agenesis and the operation of vulvavaginaplasty.

Adolescent↗
PubMed1975

Abnormal spontaneous rosette formation and rosette inhibition in lung carcinoma.

Fifty-five children with CID and known ADA status were studies at a workshop held in Albany, New York. Erythrocyte ADA determinations were performed in 22 of the 55 patients, 13 of whom were ADA negative. The ADA defect appears to be transmitted as an autosomal recessive trait. Some patients with CID and ADA deficiency have characteristic radiologic abnormalities of the skeleton, which are not found in other illnesses. The thymus glands of all patients with CID and ADA deficiency who could be examined have evidence of thymic involution manifested by presence of Hassall's corpuscles and differentiated germinal epithelium; this is in contrast to "classic" thymus findings in CID with normal ADA. Adenosine deaminase probably plays an important, although as yet undefined, role in lymphocyte development and/or function. The deficiency of ADA in CID is the first enzyme defect observed in a deficiency disease of specific immunity.

Aged↗
PubMedDate not supplied

Characterization of strains of Helicobacter pylori: one-dimensional SDS-PAGE as a molecular epidemiologic tool.

One-dimensional linear sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total proteins, coupled with a computerized numerical analysis, was used to distinguish among strains of Helicobacter pylori. One hundred seventy-five clinical strains and five reference strains of H. pylori from humans, four isolates of Helicobacter mustelae from ferrets, and three isolates of H. pylori-like organisms (HPLOs) from miniature swine were examined. Intraspecies and interspecies comparisons were made through a numerical analysis of protein profiles. It was possible to make valid comparisons for strains run on a single gel. However, variations between gels were significant in some cases, and strains from these gels were not compared. Multiple isolates of H. pylori from one patient clustered at greater than 90% similarity. All strains of H. pylori clustered at greater than 60% similarity, whereas H. pylori was clearly distinguishable (less than 40% similarity) from both H. mustelae and HPLOs. An eventual application of this technique will be to determine whether relapse following therapeutic intervention is due to reinfection (from an exogenous source) or to recrudescence.

Animals↗