Rennin enzyme of Endothia parasitica.

A microbiological screening program was instituted to search for an animal rennet substitute. Among 381 bacteria and 540 fungi tested, only one organism, Endothia parasitica, yielded a suitable enzyme substitute. The fungal rennin enzyme was crystallized and some of its properties were studied. It was found to be water-soluble, nondialyzable, precipitable with (NH(4))(2)SO(4) and organic solvents (e.g., acetone and isopropanol), and destroyed by heating for 5 min at 60 C. It was determined to be most stable in water at pH 4.5 and to have an isoelectric point of pH 5.5. On acid hydrolysis, it yielded: alanine, ammonia, arginine, aspartic acid, cysteic acid, cystine, glutamic acid, glycine, histidine, isoleucine, leucine, phenylalanine, proline, serine, threonine, tyrosine, and valine. No tryptophan was detected after alkaline hydrolysis. Its molecular weight was estimated to be in the range of 34,000 to 39,000. The milk-clotting activities of the fungal and animal rennins proved to be essentially identical in milk containing various concentrations of CaCl(2). Both rennins manifested comparable clotting activities in milk at pH 6.0 to 7.0.