Fibrinolytic enzymes from the venoms of Agkistrodon contortrix contortrix and Crotalus basiliscus basiliscus: cleavage site specificity towards the alpha-chain of fibrin.

Zinc metalloproteinases with fibrinolytic activity have been isolated from the venom of Agkistrodon contortrix contortrix (fibrolase) and Crotalus basiliscus basiliscus (basiliscusfibrases 1, 2 and 3). Fibrolase cleaves the A alpha-chain of fibrinogen initially at a single site: Lys413-Leu. Basiliscusfibrases 1, 2 and 3 also cleave at this site as well as others. Since cleavage in Lys-Leu locations is not common among zinc metalloproteinases, we examined the degree to which the Lys-Leu bond determines cleavage specificity and cleavage rates for these enzymes. We employed the oxidized B-chain of insulin and the following synthetic octapeptides: InsA (Leu-Val-Glu-Ala-Leu-Tyr-Leu-Val) which includes the insulin B-chain sequence around the Ala14-Leu15 bond (which is cleaved by all of the enzymes); InsK (Leu-Val-Glu-Lys-Leu-Tyr-Leu-Val) which is identical to InsA apart from the Ala4 to Lys4 substitution; and PA alpha (His-Thr-Glu-Lys-Leu-Val-Thr-Ser) which reproduces the sequence around the Lys413-Leu414 cleavage site of the A alpha-chain of fibrinogen. Results suggest that fibrolase is better adapted for cleaving the A alpha-chain at the Lys413-Leu414 locus and that cleavage specificity for the enzymes tested was not dictated by the Lys-Leu bond per se, but by the surrounding sequence.