(The) physiological eole of bovine kidney γ-glytamyl transpeptidase

Abstract

Membrane bound $\gamma$ -GTP was purified from bovine kidne. The first purification method includes bromelain solublization acetone precipitation, salting out, DEAE-cellulose and Sehadex G-100 column chromatogtraphies. The purification folds and ield were 44.3 and 11.9\%, respectively. The second procedure includes microsome separation, Trition x-100 solublization, acetone treatment, gel filtration on Sephacryl S-300, and adsorption chromatography on hydroxyapetite column. The enzyme was purified by 393 folds and the yield was 18.6\%. The enzyme has a substrate specificity to $\gamma$ -glutamyl peptides and Sblocked $\gamma$ -glutamyl dipeptides were the best substrate among peptides tested. Dipeptides with glycine at its C-terminal end were bettter acceptros than other peptides. Among amino acids tested, methionine, cstein and glutamine can act as acceptors. Double reciprocal plots of the reaction velocities against varing the concentration of $\gamma$ -glutaml-p-nitroanilide at three fixed concentrations of glycylglycine showed parallel pattern. In vitro and in vivo $\gamma$ -GTP mediated amino acid transports were studied. Liposome incorporated with $\gamma$ -GTP didn``t transport methionine, alanine and leucine though methionine was a good acceptor among amino acids. In vivo experiments using unilaterial renal artery infusion also didn``t show any evidences that this enzyme participates in the amino acid translocation. The unilateral inection of $\gamma$ -GTP inhibitors (DON or Acivicine) or p-amino-hippurate induced a rise in pH of urine. The enzyme was activated by its own substrate in the absence of acceptor molecule but substrate activation disappeared in the presence of maleate or glyclglycine. At high concentrations of glcylglcine, product inhibition pattern was obsrved only in the presence of maleic acid. The $\gamma$ -GTP activity was inhibited competitively b maleate and the phenomena arised by was inhibited competitively by maleate and the phenome...