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T A Lewis

Publications and source records attributed to T A Lewis.

26 records · Page 2Linked to original sources
PubMed1985

Yeast sterols: yeast mutants as tools for the study of sterol metabolism.

Yeast mutants defective in ergosterol synthesis are valuable tools for investigating sterol metabolism. Both sterol mutants and sterol auxotrophs have been utilized in determining what sterol structural features are required for yeast cell viability. Both types of mutants can also be studied to ascertain how changes in sterol structure affect membrane properties. Other aspects of sterol metabolism, such as the specificity of sterol esterification, have been elucidated by the sterol auxotrophs. In broader applications, interrelationships between sterol metabolism and other cellular functions (e.g., heme metabolism) may also be examined with these mutants. By analyzing the lipid composition of the sterol mutants, on the other hand, much of the ergosterol biosynthetic pathway has been delineated. The unusual sterols of the mutants can also be obtained to develop assays for the enzymes involved in ergosterol synthesis. Thus, by utilizing mutants, the simple eukaryotic system of yeast may be extended to explore the entire field of sterol metabolism and its relationship to cellular physiology.

Chromatography, High Pressure Liquid↗
PubMed1985

Involvement of heme biosynthesis in control of sterol uptake by Saccharomyces cerevisiae.

Wild-type Saccharomyces cerevisiae do not accumulate exogenous sterols under aerobic conditions, and a mutant allele conferring sterol auxotrophy (erg7) could be isolated only in strains with a heme deficiency. delta-Aminolevulinic acid (ALA) fed to a hem1 (ALA synthetase-) erg7 (2,3-oxidosqualene cyclase-) sterol-auxotrophic strain of S. cerevisiae inhibited sterol uptake, and growth was negatively affected when intracellular sterol was depleted. The inhibition of sterol uptake (and growth of sterol auxotrophs) by ALA was dependent on the ability to synthesize heme from ALA. A procedure was developed which allowed selection of strains which would take up exogenous sterols but had no apparent defect in heme or ergosterol biosynthesis. One of these sterol uptake control mutants possessed an allele which allowed phenotypic expression of sterol auxotrophy in a heme-competent background.

5-Aminolevulinate Synthetase↗
PubMed1979

The physiologic hyperparathyroidism of pregnancy. Is it primary or secondary?

Controversy exists over whether the increase in maternal serum parathyroid hormone levels observed during the second half of pregnancy is due to autonomous parathyroid function or is secondary to changes in maternal serum ionized calcium levels. In order to study this problem further, 9 subjects were followed serially throughout normal pregnancy. Total serum calcium, ionized calcium, parathyroid hormone (PTH), calcitonin, and albumin levels were measured monthly. Six of these subjects had the studies repeated 6 weeks postpartum. Serum ionized calcium levels were found to decrease from 3.81 +/- 0.12 mg/dl to 3.63 +/- 0.18 mg/dl between 21 and 25 weeks' gestation. This decrease was significant at P less than 0.01. The ionized calcium remained in this lower range until term. A significant return to 3.77 +/- 0.1 mg/dl was observed 6 weeks postpartum. Serum PTH levels showed a significant rise after 21 weeks' gestation (P less than 0.05). No serial change in serum calcitonin was observed during pregnancy, although the mean level of the group was significantly higher than in nonpregnant controls (P less than 0.01). The increase in maternal serum PTH observed during pregnancy appears to be due in part to a decrease in maternal serum ionized calcium.

Adolescent↗
PubMed1979

Postpartum hypokalemic paralysis.

An attack of hypokalemic paralysis occurring in a 23-year-old woman during the immediate postpartum period of her fourth pregnancy is described. A flaccid paralysis of her extremities and markedly diminished deep tendon reflexes developed 3 hours after delivery, at which time her serum potassium level was found to be 1.7 mEq/liter. Hypokalemic paralysis has not been previously reported as an immediate postpartum complication. The pathophysiology and management of this condition are discussed, as are the treatment and follow-up of this specific patient.

Adult↗
PubMedDate not supplied

2,4,6-Trinitrotoluene (TNT) transformation by clostridia isolated from a munition-fed bioreactor: comparison with non-adapted bacteria.

Several bacterial strains were examined for their ability to degrade the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). The strains examined included various clostridial strains isolated from a 4-year-old munition enrichment, related clostridial strains obtained from a culture collection, two enteric bacteria, and three lactobacilli. All Clostridium species tested were able to reduce TNT rapidly in a complex medium. In cell suspension experiments, these strains were also able to reduce 2,4-diamino-6-nitrotoluene (DANT) to 2,4,6-triaminotoluene (TAT) and to produce a compound that is not yet identified; thus, they could not be distinguished from one another with regard to the pathway of transformation. The enteric strains and the lactobacilli were able to perform the initial reduction of TNT, but none was capable of reducing DANT in cell suspensions.

Bacteriological Techniques↗
PubMedDate not supplied

Advances in migraine management.

New drugs and better understanding of the pathogenesis of migraine are improving the outlook for patients with this debilitating disorder. This paper reviews recent advances and outlines our approach.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Advances in cluster headache management.

Cluster headache, an uncommon, excruciating headache distinct from migraine, is often misdiagnosed. Until recently, therapy was difficult, but verapamil has revolutionized treatment.

Cluster Headache↗