Proteases in Blood Platelets: Collagen Induced Activation of Proelastase by a Trypsin-Like Enzymes

Arterial elastolysis is an important feature of atherosclerosis and the comprehension of the activation mechanism of platelet elastase (proelastase) is essential to the knowledge of the role of platelet proteases as an agent of vascular alterations. Trypsin, chymotrypsin and elastase-like proteases were purified from a platelet protein fraction by a three step affinity chromatography procedure. Three electrophoretically homogenous proteins of molecular weights equal to 40 × 10³ (trypsin), 32 × 10³ (chymotrypsin) and 26 × 10³ (elastase) daltons were obtained. Proelastase is strongly activated by the purified trypsin-like enzyme, whereas the chymotrypsin-1ike enzyme is ineffective. After the separation of platelet organelles on a discontinuous sucrose gradient proelastase, elastase and trypsin were found associated with the light granules and membranes. Fibrillar collagen incubated with platelets produces a rapid activation of proelastase ; elastase is then released in its active form. This effect of collagen is likely indirect and may involve an intermediary step during which proelastase becomes available to the trypsin-like enzyme.

 

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