Investigations on the activation of bovine prochymosin.

Activation of prochymosin at pH below 2.5 results in formation of the active enzyme pseudochymosin by proteolytic cleavage of the bond 27--28. Pseudochymosin is 15 amino acid residues longer than chymosin. It is the final activation product at low pH, whereas chymosin is formed by activation between pH 4 and 5. Pseudochymosin is converted to chymosin when it is brought to pH 5.5. Our present knowledge does not allow quantitative evaluation of the possible reactions involved in formation of pseudochymosin, but the course of activation at pH 2 is in accordance with an intermolecular reaction between two zymogen molecules as the predominant reaction. We find indications of an intramolecular reaction when intermolecular reactions are prevented by immobilization of the zymogen.