Studies on the peptide bond specificity and the essential groups of an acid proteinase from Aspergillus fumigatus.

The specificity and mode of action of an acid proteinase from A. fumigatus was studied with B-chain of insulin, angiotensin II and bradykinin. With reference to the known structure of the B-chain of insulin and angiotensin II, the major sites of action were determined. Acid proteinase of A. fumigatus hydrolyzed primarily three peptide bonds in the B-chain of insulin viz. i. His(5)-Leu(6); ii. Tyr(16)-Leu(17) and iii. Phe(24)-Phe(25) bonds. Additional cleavages of the bonds His(10)-Leu(11) and Leu(15-Tyr(16) were also noted. Primary splitting sites, Tyr(16)-Leu(17) and Phe(24)-Phe(25) were identical with those reported in the work of porcine pepsin C (EC 3.4.23.3). Hydrolysis of angiotensin II was observed at Tyr(4)-Ile(5) bond. The acid proteinase was found not to be inactivated by EDTA, DEP and PCMB. The pepsin specific inhibitors viz. DAN/Cu II and EPNP showed quite appreciable inhibition, while SDS completely inactivated this acid proteinase.