Purification of Rennin from Commercial Rennin Extract: Properties of Purified Product

Abstract

The purity of the enzyme, especially with respect to its contamination with pepsin, is of essential importance in understanding the biochemistry of the coagulation of milk by true rennin.Many investigations have been conducted on this general problem from which erroneous conclusions may have been drawn because of the mixed nature of the enzymes in the rennin preparations used.Several attempts to purify this enzyme have been reported but the properties of the purified products do not show ~nuch agreement except a marked increase in milk clotting activity in comparison with the crude starting material.Fenger (1), starting with dried, defatted, powdered calves' stomach mucosa, obtained a product containing 14.00 per cent N, which precipitated from dilute NaC1 solution at ptI about 3.54.0 and which readily dialyzed through parchment, tie regarded the purified rennin as a decomposition product of an acid albumin.Its milk clotting activity at 40 ° C. in 10 minutes, using sweet, certified milk (1: 2,310,000) was 770 times that of the original dried mucosa and its peptic activity (1 : 600 by the U.S.P. method) only 1.7 times that of the starting material.Liiers and Bader (2), starting with sodium phosphate solution extracts of the lead proteinatc obtained from sodium acetate extracts of calves' stomach mucosa, purified the rennin by a series of adsorptions on alumina and kaolin and elutions by phosphate buffer.Milk clotting activity was calculated from viscosity determination made at 35 ° C. for 40 minute activity time (actual time two minutes) and peptic activity was measured by a turbidometric procedure which is stated to estimate about 0.2 rag.pepsin.The most active rennin preparation contained only 0.687 per cent N and the milk clotting activity of the dry substance was calculated to be 1:16,440,000 parts of a boiled, reconstituted