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.[1]References
- Cathepsin A-like activity in thrombin-activated human platelets. Substrate specificity, pH dependence, and inhibitory profile. Ostrowska, H. Thromb. Res. (1997) [Pubmed]
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