Cathepsin A-like activity in thrombin-activated human platelets. Substrate specificity, pH dependence, and inhibitory profile.
Cathepsin A-like enzyme released from human platelets by thrombin hydrolyzed at the highest rate Cbz-Phe-Ala, Cbz-Phe-Met and Cbz-Phe-Leu, did not require activators and was inhibited by DFP, DCI and mercurial compounds (mersalyl acid, PCMS, PCMB and HgCl2). The optimum activity of secreted enzyme was at pH 5.0-6.0. Cbz-Glu-Tyr was also hydrolyzed at lower pH with optimum at pH 3.5. These enzymatic properties are the same as those of cathepsin A solubilized from whole platelets and purified from other mammalian cells and tissues. High specific activity of secreted cathepsin A, and a broad pH range of activity may have a significance in extracellular proteolysis in local sites of ischemia. Large portion of cathepsin A-like activity was not secretable by high concentration of thrombin and was sedimented with platelet aggregates. No activity of lysosomal carboxypeptidases B and prolylcarboxypeptidase was detectable in supernatants and pellets of thrombin-stimulated platelets.
Ostrowska
H
H
Department of Instrumental Analysis, Medical Academy, Bialystok, Poland.
D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology*; D043424:Carboxypeptidase B; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000097:blood* / Q000378:metabolism; D043402:Cathepsin A; D004151:Dipeptides / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008247:Lysosomes / Q000201:enzymology; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D013379:Substrate Specificity; D013917:Thrombin / Q000494:pharmacology*
D004151:Dipeptides; D002268:Carboxypeptidases; C022448:lysosomal Pro-X carboxypeptidase; C468629:CTSA protein, human; D043402:Cathepsin A; D043424:Carboxypeptidase B; D013917:Thrombin