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Biomedical subjects

S S Tate

Publications and source records attributed to S S Tate.

89 records · Page 5Linked to original sources
PubMed1972

Decarboxylation of 3,4-dihydroxyphenylalanine (DOPA) by erythrocytes: a reaction promoted by methemoglobin and other ferriheme proteins.

The decarboxylation of DOPA by erythrocyte hemolysates differs from DOPA decarboxylation catalyzed by aromatic aminoacid decarboxylases that contain vitamin B(6) in several significant respects. The ability of erythrocyte hemolysates to decarboxylate DOPA is associated with interaction between DOPA and methemoglobin; the ferriheme protein is reduced and DOPA is decarboxylated, probably after oxidation to a quinone intermediate. An analogous reaction takes place between DOPA and other ferriheme proteins, such as metmyoglobin and cytochrome c. This phenomenon may be of significance in relation to the side effects observed in patients with Parkinson's disease who are treated with very large doses of DOPA.

Animals↗
PubMed1971

Regulation of rat liver glutamine synthetase: activation by alpha-ketoglutarate and inhibition by glycine, alanine, and carbamyl phosphate.

Rat liver glutamine synthetase (s(20,w) 15.0 S; MW about 352,000) resembles ovine brain glutamine synthetase in that it (a) has 8 subunits, (b) acts on both L- and D-glutamate and certain glutamate analogs (e.g., beta-glutamate, cis-cycloglutamate, and alpha-methyl-L-glutamate), and (c) is irreversibly inhibited by L-methionine-S-sulfoximine. The liver enzyme (but not the brain enzyme) is (a) markedly activated by alpha-ketoglutarate and less so by citrate, and (b) inhibited noncumulatively by glycine and alanine, in the presence of Mn(++) but not Mg(++); inhibition increases with increasing concentrations of glutamate. These regulatory phenomena seem to be correlated with metabolically related enzymes, e.g., glutamine transaminase. Both liver and brain glutamine synthetases are inhibited by carbamyl phosphate (with Mn(++) but not with Mg(++)), which provides a means for controlling glutamine for pyrimidine biosynthesis. Addition of Mn(++) to the Mg(++)-synthetase system, even at Mg(++): Mn(++) ratios of 1000, markedly inhibits synthesis by both brain and liver enzymes. This finding, and the fact that Mn(++) promotes sensitivity to the negative effectors, indicates that Mn(++) plays a central role in the regulation of glutamine synthetase. Properties of the glutamine synthetases that have been isolated from mammalian, plant, and bacterial cells are compared. They are similar with respect to subunit size, substrate specificity, inhibition by methionine sulfoximine, and Mn(++)-sensitive inhibition by glycine, alanine, and carbamyl phosphate, but differ in certain other regulatory phenomena and in subunit structure.

Alanine↗
PubMed1971

Decrease of the 3,4-dihydroxyphenylalanine (DOPA) decarboxylase activities in human erythrocytes and mouse tissues after administration of DOPA.

Human erythrocytes have been found to contain appreciable amounts of DOPA decarboxylase (EC 4.1.1.26) activity. The enzyme activity in erythrocytes from patients with Parkinson's disease who were treated with DOPA was significantly lower than that of untreated patients and of normal individuals. Administration of the drug to mice led to a marked decrease of DOPA decarboxylase in liver and kidney, but not of the brain enzyme. The findings thus indicate that administration of DOPA leads to a decrease in peripheral DOPA decarboxylase, an effect that is expected to be of benefit in DOPA therapy of patients with Parkinson's disease. Peripheral DOPA decarboxylase concentration also decreases in mice after short periods of fasting; the findings suggest that the peripheral enzyme activities may be affected by various nutritional and perhaps hormonal influences, which may be partially responsible for the observed fluctuations in the motor abilities of Parkinsonian patients receiving constant doses of the drug. Study of DOPA decarboxylase activity in erythrocytes may be useful in following changes in patients receiving DOPA therapy and may also be of general interest and value in investigations of catecholamine metabolism in man.

Age Factors↗