Glutathione-degrading enzymes of microvillus membranes.
Microvillus membranes from rat kidney, jejunum, and epididymis have been purified by the Ca precipitation method. The membranes exhibit enrichment in specific activities of gamma-glutamyl transpeptidase, aminopeptidase M, and a dipeptidase. The latter has been characterized and shown to be the principal activity responsible for the hydrolysis of S derivatives of Cys-Gly (including cystinyl-bis-glycine (Cys-bis-Gly) and 5-hydroxy-6-S-cysteinylglycyl-1-7,9-trans-11,14-cis-eicosatetraenoic acid (leukotriene D4)). A method is described for the simultaneous purification of papain-solubilized forms of the three enzymes from renal microvilli. Dipeptidase (Mr = 105,000) appears to be a zinc metalloprotein composed of two Mr = 50,000 subunits. The enzyme is severalfold more effective in the hydrolysis of dipeptides than aminopeptidase M. Dipeptidase, in contrast to aminopeptidase M, is inhibited by thiol compounds; Cys-Gly, in particular, is a potent inhibitor (Ki = 20 microM). The inhibition of dipeptidase by thiols has been employed to probe the relative significance of dipeptidase and aminopeptidase M in the metabolism of glutathione and its derivatives at the membrane surface.
D000469:Alkaline Phosphatase / Q000378:metabolism; D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D018826:CD13 Antigens; D002462:Cell Membrane / Q000201:enzymology*; D004150:Dipeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004822:Epididymis / Q000201:enzymology*; D005978:Glutathione / Q000378:metabolism*; D007583:Jejunum / Q000201:enzymology*; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D008871:Microvilli / Q000201:enzymology*; D051381:Rats; D013379:Substrate Specificity; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D005723:gamma-Glutamyltransferase; D000469:Alkaline Phosphatase; D000626:Aminopeptidases; D018826:CD13 Antigens; D004150:Dipeptidases; D005978:Glutathione