Inhibition of platelet thromboxane synthetase by L-1-tosylamido-2-phenylethyl chloromethyl ketone

L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK) was found to inhibit several aspects of arachidonic acid (20:4) metabolism in human platelets; the primary effect being inhibition of thromboxane synthetase. Thromboxane B₂ (TxB₂) formation from exogenous 20:4 or PGH₂, or from endogenous 20:4, was inhibited by TPCK at concentrations between 0.1 and 0.5 mM. Formation of malondialdehyde (MDA) and 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT), products which also arise from PGH₂, was inhibited to a similar extent. Inhibition of formation from 20:4 of 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE), the product of the lipoxygenase pathway, was observed; although the extent of this inhibition was less than that of TxB₂ formation. A small inhibitory effect of TPCK on the release of 20:4 from platelet phospholipids was also observed. This evidence indicated that while a number of reactions are inhibited by TPCK, the primary effect appears to be inhibition of thromboxane synthetase.