Interaction of gamma-glutamyl transpeptidase from eri-silk-worm mid-gut with different substrates and its possible physiological role

Interaction of gamma-glutamyl transpeptidase from eri-silk-worm mid-gut with different substrates and its possible physiological role

1990

REP.G0647

The highly purified gamma-glutamyltranspeptidase preparation from the mid-gut of eri-silkworm Philosamia cynthia ricini was examined with respect to its specificty toward different gamma-glutamyl donors and acceptors. Of the 20 amino acids tested, phenylalanine, methionine, cystine, tryptophene, arginine and lysine were the best acceptors of the gamma-glutamyl group, whereas glutamine and glutamate bound effectively to the gamma-glutamyl binding site. The Km values for gamma-glutamyl-p-nitroaniline are 0.13 mmol/L with phenylalanine and 0.29 mmol/L without phenylalanine. The competitive fnhibition constant Ki values for glutathione and glutamine are 0.5 and 1.1 mmol/L respectively in the presence of phenylalanine. The enzyme catalyzes the utilizatioh of glutamine by conversion to glutamate, ammonia and gamma-glutamyl-L-amino acids at about 38% Of the rate observed for catalysis of releasing p-nitroaniline from gamma-glutamyl-p-nitroaniline. The participation of the enzyme in the absorption and transportation of some indispensable amino acids in the mid-gut of the silkworm is discugsed.

v.33(2):136-142, ACTA ENTOMOLOGICA SINICA

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