The primary structure of calf chymosin.

The complete amino acid sequence of calf chymosin (rennin) (EC 3.4.23.4) has been determined. The sequence consists of a single peptide chain of 323 amino acid residues. The primary structure of the precursor part of calf prochymosin was published previously (Pedersen, V.B., and Foltmann, B. (1975) Eur. J. Biochem. 55, 95-103), thus we are now able to account for the total 365 amino acid residues of calf prochymosin. Comparison of the sequence of calf prochymosin with that of pig pepsinogen A (EC 3.4.23.1) shows extensive homology. In the precursor part of the sequence, 15 residues are located at identical positions, as compared to 189 identical residues in the respective enzymes. Furthermore comparison to Penicillium janthinellum acid proteinase (penicillopepsin) (EC 3.4.23.7) shows that 76 residues are common to this enzyme and to the two gastric proteinases. These homologies in sequence further suggest that the folding of the peptide chain in chymosin is very similar to that of other acid proteinases.