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Biomedical subjects

D Watkins

Publications and source records attributed to D Watkins.

At least 73 records · Page 4Linked to original sources
PubMed1988

Genetic heterogeneity among patients with methylcobalamin deficiency. Definition of two complementation groups, cblE and cblG.

A number of patients with megaloblastic anemia and homocystinuria associated with low levels of methylcobalamin synthesis in cultured cells have been recognized. Methionine biosynthesis by intact cells, as determined by incorporation of label from 5-[14C]methyl-tetrahydrofolate into acid-precipitable material, was deficient in cultured skin fibroblasts that were derived from all of these patients. In one group of patients, activity of the methylcobalamin-dependent enzyme, methionine synthase, in cell extracts was within the normal range when the enzyme was assayed under standard conditions. In a second group of patients, methionine synthase activity was decreased under the same assay conditions. Genetic complementation analysis demonstrated the existence of two complementation classes that corresponded to these two groups of patients. The designation cblE has previously been proposed for normal methionine synthase activity. We propose the designation cblG for the mutation in those patients with methylcobalamin deficiency and decreased synthase activity. The results of these studies suggest that the products of at least two loci are required for cobalamin-dependent methionine biosynthesis in mammalian cells.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1988

The ontogeny of interleukin production and responsivity in the frog, Xenopus.

The production of and responsivity to leukocyte-derived lymphokine-rich culture supernatants (SNs) was examined during the ontogeny of the frog, Xenopus. Thymocytes and splenocytes from adult frogs are capable of responding to the T-cell mitogen, phytohemagglutinin-P (PHA). Larval thymocytes are unresponsive to this lectin, whereas larval splenocytes are not. PHA-unresponsive thymocytes can be costimulated with PHA plus either a T-cell growth factor (TCGF)-rich SN or an interleukin-1 (IL-1)-rich SN (from cultures of lipopolysaccharide (LPS)-treated macrophage-enriched peritoneal cells (PCs). Stimulation of larval thymocytes with PHA does not produce a TCGF-rich SN as assayed by proliferation of lymphoblasts. Larval as well as adult splenocytes treated with PHA, however, do produce TCGF. These data are consistent with the hypothesis that the factor limiting mitogen responsiveness of larval thymocytes is the ability of cell populations in the thymus to produce rather than respond to either IL-1 or IL-2.

Animals↗
PubMed1987

Vitamin B12 responsive homocystinuria and megaloblastic anemia: heterogeneity in methylcobalamin deficiency.

A male infant with methyl-B12 deficiency (cblE) presented at age 6 weeks with lethargy, staring spells, and vomiting. He later became hypotonic and unresponsive to stimuli and required intubation and ventilation. He had homocystinuria and hypomethioninemia with megaloblastic anemia but normal serum folate and vitamin B12 concentrations. No methylmalonic aciduria was detected. Fibroblasts, cultured from the patient, were unable to grow in medium in which homocysteine replaced methionine and incorporated abnormally small amounts of [14C]-methyl-tetrahydrofolate but normal amounts of [14C]-propionate into protein. Methyl-B12 content of fibroblasts was low, while the adenosyl-B12 content was normal. Methionine synthase activity was decreased when the assay was performed under both optimal and suboptimal reducing conditions, suggesting heterogeneity in the cblE disease. The patient responded dramatically to hydroxocobalamin treatment. Homocystinuria disappeared after 10 days of therapy, and methionine was normalized after 3 weeks. Psychometric testing at age 15 months showed a developmental age of 9 months.

Anemia, Macrocytic↗
PubMed1987

Mitogen-activated Xenopus laevis lymphocytes produce a T-cell growth factor.

Mitogen-free and serum-free supernatants (SNs) from cultures of phytohaemagglutinin (PHA)-stimulated Xenopus splenocytes, co-stimulated thymocytes, induced proliferation of splenic and thymic lymphoblast and supported growth of alloreactive T-cell lines. These SNs had no effect on 'resting' splenocytes, as measured by uptake of tritiated thymidine ([3H]TdR). Growth-promoting activity was also detected in SNs of cultures containing alloreactive T-cell lines and either PHA or irradiated stimulator cells that expressed the original priming alloantigens. Thus, T lymphocytes appear to be involved in producing, as well as responding to, a Xenopus T-cell growth factor (TCGF). TCGF activity could be absorbed from these active SNs with PHA-activated splenic blasts. No functional cross-reactivity among different mammalian interleukin-2 (IL-2) and Xenopus TCGF preparations was detected.

Animals↗
PubMed1987

A factor with interleukin-1-like activity is produced by peritoneal cells from the frog, Xenopus laevis.

Thymocytes from juevenile Xenopus laevis did not proliferate in response to commercial preparations of lipopolysaccharide (LPS), responded poorly when cultured with the T-cell mitogen, phytohaemagglutinin-P (PHA), and were not co-stimulated by PHA plus LPS. However, supernatants (SNs) from LPS-treated cultures of adult Xenopus macrophage-enriched resident peritoneal cells (PCs) enhanced the proliferative responses of thymocytes to a submitogenic dose of PHA. These SNs were incapable of supporting long-term growth of thymic lymphoblast cell lines, and thus could be distinguished from T-cell growth factor (TCGF)-rich SNs, which were essential for propagating these cells. The co-stimulatory activity was present in 0-24-hr SNs; after 48 hr, SN activity declined. No functional cross-reactivity of mammalian and Xenopus interleukin-1 (IL-1)-rich SNs was detected. These data are consistent with the proposition that a macrophage-derived factor, functionally homologous with mammalian IL-1, can enhance a T-cell proliferative response in an amphibian.

Animals↗
PubMed1986

Clinical heterogeneity in cobalamin C variant of combined homocystinuria and methylmalonic aciduria.

We describe two patients with methylmalonic aciduria and homocystinuria (Cbl C). The disorder was not diagnosed in patient 1 until 4 1/2 years of age; he had a history of fatigue, anorexia, delirium, and spasticity. Moderate megaloblastic bone marrow changes were observed, and there was hyperreflexia of the lower limbs. His condition improved clinically with hydroxycobalamin therapy. Patient 2 was hospitalized at 6 weeks of age because of lethargy and poor feeding. She was found to have macrocytosis. Despite an initial good clinical response to hydroxycobalamin, she developed a striking pigmentary retinopathy. Methylmalonic aciduria persisted in both patients, and homocystinuria persisted in patient 1 despite therapy. The diagnosis of Cbl C disease has been confirmed in both patients by biochemical studies of cultured fibroblasts, including complementation studies. The differences in age of onset and clinical findings together with the similar biochemical findings in these two patients demonstrate the heterogeneity of phenotypic expression in patients with apparently identical abnormalities of vitamin B12 metabolism.

Amino Acid Metabolism, Inborn Errors↗
PubMed1986

Failure of lysosomal release of vitamin B12: a new complementation group causing methylmalonic aciduria (cblF).

A patient has been described with methylmalonic aciduria because of an inability to release free vitamin B12 from lysosomes. Complementation analysis was performed using fibroblasts from this patient and those from patients having previously described mutations causing methylmalonic aciduria (mut, cblA, cblB, cblC, and cblD). Incorporation of label from [1-14C]propionate into acid-precipitable material was elevated in heterokaryons formed by polyethylene glycol (PEG) treatment of mixed cultures of cells from the patient and all other complementation groups as compared to the incorporation in parallel cultures not treated with PEG. These results indicate that complementation occurred in all cases and support the assignment of the patient to a new complementation group that has been designated cblF.

Genetic Complementation Test↗
PubMed1985

Identification and characterization of calmodulin-binding proteins in islet secretion granules.

The binding of 125I-calmodulin to intact secretion granules and protein gel blots of secretion granules from pancreatic islet tissue was examined. Binding of 125I-calmodulin to intact secretion granules was Ca2+-dependent and inhibited by the calmodulin inhibitors trifluoperazine and calmidazolium. Binding was inhibited by excess (200 nM) unlabeled calmodulin, but not by parvalbumin, a Ca2+-binding protein which has little sequence homology to calmodulin. In order to study the binding of calmodulin to specific secretion granule proteins, secretion granules were solubilized, and the solubilized proteins were resolved on sodium dodecyl sulfate-polyacrylamide gels, electrophoretically transferred to nitrocellulose, and incubated with 125I-calmodulin. Autoradiograms of the protein gel blots revealed the presence of three major calmodulin-binding proteins with approximate molecular weights of 73,000, 64,000, and 58,000. These proteins reversibly bound calmodulin in a calcium-dependent manner. Unlabeled calmodulin in the range of 0.1-1.0 nM competed with 125I-calmodulin for binding to these proteins, whereas troponin and parvalbumin were 100 and 1000-fold less effective, respectively. Trifluoperazine blocked binding to the granule proteins in a range of 10(-4) to 10(-5) M, and calmidazolium was effective between 10(-5) and 10(-6) M. Trypsin, at a concentration which did not lyse granules, markedly inhibited calmodulin binding to intact secretion granules. Protein blots from trypsin-treated granules showed that the three major calmodulin-binding proteins were absent. These results indicate that Ca2+-dependent calmodulin-binding proteins are present on the cytoplasmic surface of islet secretion granules and are consistent with the hypothesis that these proteins may play a role in secretion granule exocytosis.

Animals↗
PubMed1984

Some biochemical correlates of panic attacks with agoraphobia and their response to a new treatment.

Thirty-two patients with chronic debilitating agoraphobia and panic attacks participated in a comparative study of the triazolobenzodiazepine alprazolam and the anti-inflammatory agent ibuprofen. After a 2-week placebo washout period, patients were randomly assigned to 8 weeks of treatment with alprazolam (2 to 6 mg/day) or ibuprofen (0.8 to 2.4 g/day). Medication was identically packaged and patients were blind to the treatment condition, but investigators were aware of which medication was dispensed. Alprazolam recipients (mean daily dose: 5.4 mg) improved markedly with respect to physician and patient global rating of disease severity, frequency and severity of panic attacks, and phobic anxiety target symptoms on the 90-Item Hopkins Symptom Check List. Ibuprofen recipients (mean daily dose: 2.13 g) experienced significantly less clinical improvement than patients on alprazolam. After 8 weeks of treatment, ibuprofen patients were crossed over to alprazolam, while the original alprazolam group continued on that drug. The daily dosage ceiling was increased to 10 mg. In the ensuing 4 weeks (mean daily alprazolam dose: 6.3 mg), all patients achieved comparably marked clinical improvement relative to baseline. Pretreatment plasma concentrations of platelet factor 4 and beta-thromboglobulin--two measures of platelet turnover and release--were significantly elevated in patients relative to normal controls. The elevated platelet factor 4 and beta-thromboglobulin normalized during treatment with both drugs. Alprazolam appears to produce rapid and specific clinical improvement in patients with severe agoraphobia and panic attacks and deserves further evaluation under double-blind conditions.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

A critical intracellular concentration of fully reduced non-methylated folate polyglutamates prevents macrocytosis and diminished growth rate of human cell line K562 in culture.

Growth rate of human leukaemic cell line K562 was independent of intracellular folate concentration when this was greater than 1.5 microM. When intracellular folate concentration was less than 1.5 microM, the rate of growth was proportional to the logarithm of intracellular concentration of non-methylated fully reduced folates, but not to the logarithm of the intracellular concentration of N5-methyltetrahydropteroylglutamate. Intracellular folate concentration sufficient to support an optimal growth rate was maintained by either DL-N5-formyltetrahydropteroylglutamate or DL-N5-methyltetrahydropteroylglutamate at a 100-fold lower concentration than pteroylglutamate. Addition of hypoxanthine to culture medium partially restored growth of folate-depleted cells: thymidine had no effect on growth rate either alone or in combination with thymidine. Folate-depleted cells with diminished growth rate were larger than replete cells, but did not have megaloblastic morphology. The mitotic index was not decreased in cultures with diminished growth rate. The rate of growth and cell size of K562 cells is thus dependent on a critical intracellular concentration of non-methylated tetrahydrofolates, which may be maintained by different concentrations of either reduced folates or pteroylglutamate.

Cell Division↗
PubMed1979

The 'DNA-membrane complex' of Escherichia coli B/r. Its composition and properties and the fate of nascent and genome DNA during DNA synthesis.

The composition and properties of 'DNA-membrane complex' of Escherichia coli B/r have been investigated. The 'complexes' contain most of the DNA and membrane of the cells, and about 50% and 25% of the RNA and protein respectively. The properties of DNA synthesized by the 'complexes' are described and the process is concluded to be largely mediated through polymerase I. Nascent DNA synthesized by the 'DNA-membrane complexes' was of two main classes, one of molecular weight around 600,000--800,000 and the other of higher molecular weight. Polynucleotide ligase activity was not detectable. The onset of synthesis coincided with the dissociation of at least 70% of the genome DNA and all of the nascent DNA from the 'complexes' and was concomitant with the action of a nuclease on parental DNA. This nuclease activity was not ATP-dependent.

Adenosine Triphosphate↗