Enzymatic digestion of human plasma inter-alpha-trypsin inhibitor by snake venom metalloproteinases.

Incubation of human plasma inter-alpha-trypsin inhibitor with crotalid, viperid, colubrid or elapid venoms resulted in random cleavage of the intact inhibitor (200,000 mol. wt) and formation of inhibitor of 130,000, 77,000, 58,000, and 38,000 mol. wt, along with several minor products. The overall patterns of digestion varied among the venoms studied. However, a 77,000 mol. wt inhibitor cleavage product was formed by all venoms tested, and this fragment was resistant to proteolysis even after a 24 hr incubation with the venoms. Venom pre-treated with phenylmethylsulfonyl fluoride digested inter-alpha-trypsin inhibitor; however, pre-treatment with EDTA completely stopped the reaction, indicating that venom metalloproteinases were responsible for the inhibitor digestion. The inhibitor cleavage products retained the ability to inhibit trypsin, but had no inhibitory activity against venom proteinases.