Effects of Chymotrypsin on the Release Reaction and Aggregation of Blood Platelets

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Abstract
Human platelets incubated with chymotrypsin and washed are known to aggregate with fibrinogen. Chymotrypsin is reported to cleave platelet membrane glycoproteins without causing the release reaction seen with some proteolytic enzymes such as trypsin. Recent batches of chymotrypsin from 2 manufacturers caused platelets to release much of the contents of their dense granules, largely because they are contaminated with trypsin. Even after inhibition of trypsin with N-.alpha.-tosyl-L-lysine chloromethylketone hydrochloride (TLCK), chymotrypsin induced some release from platelets at low concentrations of ionized Ca. As expected, platelets incubated with either trypsin-contaminated or TLCK-treated chymotrypsin aggregated with fibrinogen after they were washed. Released or added ADP enhanced the release reaction and development of aggregability with fibrinogen. Fibrinogen-induced aggregation and [14C]serotonin secretion were less when released ADP was enzymatically destroyed during incubation of platelets with 500 .mu.g/ml of trypsin-contaminated chymotrypsin, and they were increased if 25 .mu.M ADP was added before incubating the platelets with 125 .mu.g/ml of this chymotrypsin.