Abstract
We have demonstrated that thrombin-induced platelet release reaction is closely related to the specific hydrolysis of glycoprotein V (GPV) which is one of the surface membrane glycoproteins and whose molecular weight is approximately 80, 000 to 90, 000 daltons.
In this study, we have further studied the influence of the other serineproteases on GP V, using trypsin and α-chymotrypsin.
GP V was hydrolyzed not only by thrombin but also by trypsin in a concentration or time-dependent manner, and its disappearance was accompanied with release reaction. Trypsin also hydrolyzed GP I (M. W. 150, 000) and high molecular weight glycoproteins as well, chymotrypsin had no effect on the membrane glycoproteins nor the release reaction.
Platelets pretreated with thrombin showed the decreased release reaction after stimulation with trypsin or thrombin, but there was no remarkable change in platelets pretreated with chymotrypsin, which have the functionally affected GP I.
Heparin had specific inhibitory effect against thromb-ininduced release reaction in a concentration dependent manner and its effect was remarkably increased by using platelets pretreated with chymotrypsin instead of normal washed platelets.
As the results, the most important glycoprotein for the serineproteases to induce release reaction was GP V, which was hydrolyzed specifically by thrombin or non-specifically by trypsin. On the other hand, it was considered that GP I was the receptors for heparin as well as for thrombin, and heparin exhibited its inhibitory effect on thrombininduced release reaction by means of competition for these receptors on GP I.
