Formation of protease nexin-thrombin complexes on the platelet surface

✍ Scribed by Robert S. Gronke; Thomas K. Curry; Joffre B. Baker

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: English
• Weight: 403 KB
• Volume: 32
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.240320306

✦ Synopsis

We have recently described a platelet factor that is similar to the fibroblast thrombin inhibitor protease nexin I (PNI) [ 121. The present manuscript shows that this platelet form of PN (PN,) does not complex ['251]-thrombin that has been blocked at its active site, consistent with the conclusion that it is a thrombin inhibitor. When platelets are incubated with [ '251]-thrombin, PN,-[ '251]-thrombin complexers accumulate both in the medium and on the platelet surface. In the case of fibroblasts, PNI-['251]-thrombin complexes that form in solution bind to the cells as a consequence of a receptor-mediated clearance process [Low et al, Proc Natl Acad Sci USA 78:2340, 19811. We show here that the PN,-['251]-thrombin complexes that accumulate in platelet-binding incubation medium do not bind to platelets. Thus, the platelet-associated complexes must form by [ '251]-thrombin binding to PN, that is associated with the platelet surface. Pretreatment of platelets with heparin markedly increases the number of PN,-[ '251]-thrombin complexes that form on platelets. The basis for this increase in unclear. This effect seems incompatible with a heparinlike factor acting as the surface binding site for PN,.