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Activation of Prorennin by Pepsin^{1, 2,}

Department of Food Science and Industries, University of Wisconsin, Madison

ABSTRACT

The ability of pepsin to catalyze the activation of prorennin was demonstrated when purified prorennin solutions buffered at pH 6.0 and 5.5 were activated by pepsin at 25 C with little interference from auto-catalytic activation by rennin. Addition of M NaCl retarded activation of prorennin by pepsin at pH 6.0 and 5.5, but the reaction was still faster than in rennin-catalyzed activation mixtures containing the same concentration of salt. Pepsin-catalyzed activation of prorennin at pH 6.0 appeared to follow zero-order kinetics during the early stages of reaction, followed by a marked change to a reduced rate of activation. However, the kinetics of activation may have been complicated by lack of pepsin stability at pH 6.0.

Pepsin was more proteolytic than rennin on casein substrates at all pH values from 2.0 to 6.0. The general proteolytic activities of rennin and pepsin as distinguished from their milk-clotting activities may be related to their respective abilities to activate prorennin. Pepsin was able to stimulate activation of crude rennet extracts at pH 5.5, where rennin has good stability. Use of pepsin in commercial rennet activation could reduce or eliminate activation losses.

¹ Published with approval of the Director, Wisconsin Agricultural Experiment Station.

² This study was supported in part by a research grant from the Research Committee of the Graduate School, University of Wisconsin, from funds supplied by the Wisconsin Alumni Research Foundation.

³ Present address: Department of Animal Science, University of Rhode Island, Kingston.

⁴ Present address: Department of Food Science and Industries, Utah State University, Logan.