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S S Tate

Publications and source records attributed to S S Tate.

At least 73 records · Page 4Linked to original sources
PubMed1977

Affinity labeling of gamma-glutamyl transpeptidase and location of the gamma-glutamyl binding site on the light subunit.

Gamma-Glutamyl transpeptidase, which consists of two nonidentical subunits, is rapidly inactivated with respect to its transpeptidase and hydrolase activities by the gamma-glutamyl analogs 6-diazo-5-oxo-L-norleucine and L-azaserine. Inactivation, which is prevented by gamma-glutamyl substrates (but not by acceptor substrates), is accelerated by maleate, which was previously shown to enhance utilization of glutamine by transpeptidase. 6-Diazo-5-oxo--norleucine reacts specifically, covalently, and stoichiometrically at the gamma-glutamyl site of the enzyme, which was localized through studies with 6-diazo-5-OXO-[14C]norleucine to the light subunits of both the transpeptidase of rat kidney (which has subunits of molecular weights 22,000 and 46,000) and the transpeptidase of human kidney (which has subunits of molecular weights 22,000 and 62,000). The findings, which indicate that these enzymes have similar gamma-glutamyl binding subunits, are relevant to the structure-function relationships of this membrane-bound enzyme and its physiological role.

Affinity Labels↗
PubMed1976

gamma-Glutamyl transpeptidase, a lymphoid cell-surface marker: relationship to blastogenesis, differentiation, and neoplasia.

gamma-Glutamyl transpeptidase, an enzyme that catalyzes gamma-glutamyl transfer from gamma-glutamyl compounds to amino acid and peptide acceptors, and which is known to be localized in the membranes of many epithelial cells, was found in a variety of lymphoid cells. The lymphoid cell enzyme is located on the cell surface, and exhibits substantially the same substrate specificity as the enzyme found in epithelial cells. Human and rat (but not mouse) lymphocyte gamma-glutamyl transpeptidase was stimulated by treatment of the cells with mitogens. Normal human peripheral B-cells were more active than T-cells, but the reverse relationship of activities was found in chronic lymphocytic leukemia lymphocytes. Human lymphoblastic lines vary markedly in activity. In general, cell lines with B- and T-characteristics from patients with lymphoproliferative diseases had much lower activities than those of B-cell lines derived from normal subjects. The highest activity found was in a human myeloma line active in synthesis of an immunoglobulin light chain. The data indicate that gamma-glutamyl transpeptidase is a surface marker reflecting differentiation in normal and neoplastic cells.

Animals↗
PubMed1976

Subunit structure and isozymic forms of gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase is associated with the membranes of a number of epithelial and lymphoid cells. When the enzyme is isolated from rat kidney by a method involving detergent extraction and affinity chromatography, an aggregate of molecular weight greater than 200,000 (heavy form) is obtained. Treatment of the heavy form with bromelain yields a light form of the enzyme (molecular weight of approximately 68,000), which is separable by isoelectric focusing into 12 enzymatically active isozymes which are very similar with respect to catalytic behavior, content of amino acids, hexoses, and aminohexoses, but which differ significantly in sialic acid content. Treatment with neuraminidase converts the acidic isozymes to more basic forms. Each isozyme dissociates in sodium dodecyl sulfate into two nonidentical glycopeptides (molecular weights of 46,000 and 22,000) which can be cross-linked with dimethylsuberimidate to yield a species with an apparent molecular weight of 70,000, which indicates that the isozymes are dimers. Physical and immunological studies indicate that the heavy form of the enzyme contains the dimeric light form as well as other membrane proteins.

Animals↗
PubMed1975

Identity of maleate-stimulated glutaminase with gamma-glutamyl transpeptidase in rat kidney.

Gamma-Glutamyl transpeptidase was purified from rat kidney by a procedure involving Lubrol extraction, acetone precipitation, ammonium sulfate fractionation, treatment with bromelain, and column chromatography on DEAE-cellulose and Sephadex G-100. The final preparation (enzyme III), which exhibits a specific activity about 8-fold higher than that of the purified rat kidney transpeptidase previously obtained in this laboratory (enzyme I), was apparently homogeneous on polyacrylamide gel electrophoresis. Enzyme III is a glycoprotein containing 10% hexose, 7% aminohexose, and 1.5% sialic acid; a tentative molecular weight value of about 70,000 was obtained by gel filtration. Enzyme III has a much lower molecular weight and a different amino acid and carbohydrate content than the less active rat kidney transpeptidase preparation previously obtained, but obtained, but the catalytic properties of these preparations are virtually identical. It is suggested that bromelain treatment may liberate the transpeptidase from a brush border complex that contains other proteins. An improved method is described for the isolation of the higher molecular weight form of the enzyme (enzyme I) in which affinity chromatography on concanavalin A-Sephrose is employed. The purified transpeptidase (enzyme III) is similar to the phosphate-independent maleate-stimulated glutaminase preparation obtained from rat kidney by Katunuma and colleagues with respect to amino acid and carbohydrate content, apparent molecular weight, and relative transpeptidase and maleate-stimulated "glutaminase" activities. Both of these enzyme preparations are much more active in transpeptidation reactions with glutathione and related gamma-glutamyl compounds than with glutamine. In the absence of maleate, the enzyme catalyzes the utilization of glutamine (by conversion to gamma-glutamylglutamine, glutamate, and ammonia) at about 2% of the rate observed for catalysis of transpeptidation between glutathione and glycylglycine; the utilization of glutamine occurs about 8 times more rapidly in the presence of 0.1 M maleate. The transpeptidation and maleate-stimulated glutaminase reactions catalyzed by both enzyme preprations are inhibited by 5 mM L-serine in the presence of 5 mM sodium borate. Studies on gamma-glutamyl transpeptidase and maleate-stimulated glutaminase in the kidneys of fetal rats, newborn rats, and rats after weaning showed parallel development of these activities. The evidence reported here and earlier work in this laboratory strongly support the conclusion that maleate-stimulated glutaminase activity is a catalytic function of gamma-glutamyl transpeptidase. The studies on the ontogeny of gamma-glutamyl transpeptidase and other data are considered in relation to the proposal that this enzyme is involved in amino acid and peptide transport. Its possible role in renal formation of ammonia is also discussed.

Aging↗
PubMed1974

Formation of 5-oxoproline from glutathione in erythrocytes by the gamma-glutamyltranspeptidase-cyclotransferase pathway.

gamma-Glutamyltranspeptidase activity was demonstrated in the membrane fraction of rabbit erythrocytes. The activity observed (with glutathione and various amino-acid acceptors) was similar in magnitude to that of the gamma-glutamylcyclotransferase and gamma-glutamylcysteine synthetase activities found in the soluble fraction of the cell. No transpeptidase activity was observed with either gamma-glutamyl p-nitroanilide or oxidized glutathione in contrast to the rabbit-kidney enzyme for which these compounds and glutathione serve as substrates. Erythrocyte suspensions and hemolysates formed 5-oxoproline (pyroglutamate; pyrrolidone carboxylate); the rate of 5-oxoproline formation from glutathione by hemolysates was increased by addition of methionine. The findings indicate that 5-oxoproline is an end-product of glutathione metabolism in erythrocytes, and that 5-oxoproline passes out of the erythrocyte and is metabolized in other tissues. The observed rate of 5-oxoproline formation is consistent with the conclusion that the gamma-glutamyltranspeptidase-cyclotransferase pathway, together with the synthesis of glutathione from glycine, cysteine, and glutamate, account for a large fraction of the observed amino-acid turnover of erythrocyte glutathione.

Acyltransferases↗
PubMed1974

Stimulation of the hydrolytic activity and decrease of the transpeptidase activity of gamma-glutamyl transpeptidase by maleate; identity of a rat kidney maleate-stimulated glutaminase and gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase catalyzes transfer of the gamma-glutamyl moiety of glutathione (and other gamma-glutamyl compounds) to amino acid and peptide acceptors; this reaction probably involves (a) formation of a gamma-glutamyl enzyme and (b) reaction of the gamma-glutamyl-enzyme with an acceptor. Maleate decreases the latter reaction and markedly increases hydrolysis of the gamma-glutamyl donor, apparently by affecting the enzyme so as to facilitate reaction of the gammaglutamyl enzyme with water. Transpeptidase catalyzes gamma-glutamyl hydroxamate formation from many gamma-glutamyl compounds and hydroxylamine; this reaction is stimulated 4- to 5-fold by maleate. Glutamine, a poor substrate for transpeptidation as compared to glutathione, is slowly hydrolyzed and converted to gamma-glutamyl-glutamine by the transpeptidase; in the presence of maleate, hydrolysis of glutamine is markedly (>10-fold) increased, as is also its conversion to gamma-glutamyl hydroxamate in the presence of hydroxylamine. The findings suggest that the previously described "maleate-stimulated phosphate-independent glutaminase" is a catalytic function of gamma-glutamyl transpeptidase. Transpeptidase-catalyzed glutaminase activity may play a role in renal ammoniagenesis. The ability of maleate to decrease transpeptidation of gamma-glutamyl compounds (and to increase their hydrolysis to glutamate), when considered in the light of earlier findings that treatment of animals with maleate produces aminoaciduria, is consistent with function of transpeptidase and the gamma-glutamyl cycle in amino-acid transport.

Ammonia↗
PubMed1973

The -glutamyl cycle in the choroid plexus: its possible function in amino acid transport.

Various anatomic regions of rabbit brain have been examined for activities of the enzymes of the gamma-glutamyl cycle. While these enzyme activities were widely distributed in the brain, they are present in much higher concentrations in the choroid plexus than in other parts of the brain. The activities observed are of about the same order of magnitude as found in the kidney. These observations and other considerations suggest that the gamma-glutamyl cycle may play a significant role in the transport of amino acids between blood and cerebrospinal fluid.

Acyltransferases↗
PubMed1973

Enzymes of the gamma-glutamyl cycle in the ciliary body and lens.

The enzymes of the gamma-glutamyl cycle have been found in rabbit ciliary body and, except for 5-oxoprolinase, also in the ocular lens. Histochemical studies show that gamma-glutamyl transpeptidase is localized mainly in the basal portions of the epithelial cells of the ciliary body; the findings are similar to those observed in the chloroid plexuses. The histochemical staining reaction in the ciliary epithelium is more intense than in the chloroid plexus, intestine, and kidney. gamma-Glutamyl transpeptidase staining activity in the epithelium of the intestinal and renal proximal convoluted tubules is confined to the microvillus border. Moderate transpeptidase activity was found in the cytoplasm of nonpigmented epithelial cells of the iris at the posterior pupillary margin. The histochemical and enzyme activity studies are consistent with the thesis that the gamma-glutamyl cycle functions in transport of amino acids across the blood-aqueous humor barrier.

Acyltransferases↗