Glutamyl Transpeptidases from Kidney

The ability of enzyme preparations from various animal tissues to catalyze transfer of the glutamyl unit from glutamine or glutathione to certain a-amino acids and peptides, first observed by Hanes et al. (38), has been examined in several laboratories (32, 35, 39-41). Enzymes of this type have been studied recently by Orlowski and Meister (in hog kidney) (32) and by Szewczuk and Baranowski (in beef kidney) (41)-Results with the hog kidney enzyme will be reviewed here the beef enzyme is quite similar in many respects, but it is not identical in physical properties. 

After solubilization from a particulate fraction of hog kidney cortex, the transpeptidase has been obtained in highly purified, but not yet homogeneous, form. The enzyme is active in the alkaline pH region with a maximum at about pH 8.8. Although appreciable magnesium is present in the enzyme preparation and added Mg2+ partially stimulates the catalytic action, it is not certain whether this metal is essential for activity since EDTA exerts an enhancement rather than an inhibition. 

If one of a large number of a-amino acids or peptides is present, it 

Neither glutamine nor glutamyl naphthylamide are substrates. The specificity requirements for the acceptor are considerably more demanding in that acyl transfer to water (hydrolysis) or to hydroxylamine is not observed under any conditions. The transferase was separated chromatographically from an enzyme capable of hydrolyzing glutamyl naphthylamide which conceivably is related to the previously described transpeptidase. 

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Goore, M. Y., and J. F. Thompson y-Glutamyl transpeptidase from kidney bean fruit. I. Purification and mechanism of action. Biochim. Biophys. Acta 132, 15 (1967). 

Reaction with amine acceptors preferred. Hydrolysis of glutamyl compounds occurs with the transferase from mushrooms 31) and with one type of transpeptidase isolated from kidney 32). However, when suitable amine acceptors are present the hydrolytic reaction is largely suppressed in favor of transfer to the amine. 

Attempts have been made to develop noninvasive tests that might provide more specific information about the site of injury. For example, excretion of enzymes in urine may reflect renal injury. Urinary excretion of enzymes of renal origin (enzymes that are specific to the kidney, such as maltase, y-glutamyl transpeptidase, or treha-lase) could indicate specific destruction of renal proximal tubules, whereas alkaline phosphatase in urine could arise from renal or prerenal (e.g., hepatic) damage (Figure 29.7). 

S-alkyl cysteines, such as S-allyl cysteine (SAC), S-methyl cysteine (SMC), and S-propyl cysteines are slowly formed during sprouting from the action of y-glutamyl transpeptidase on y-glutamyl cysteines. S-allyl cysteine is also rapidly formed in the body by hydrolysis of y-glutamyl cysteine particularly in the kidney which contains an abundant amount of Y-glutamyl transpeptidase activity [2]. 

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