Multiple forms of calf prochymosin and chymosin

Recent advances in milk clotting enzymes

“…Calf chymosin is expressed in two major allelic forms of a single gene locus, which differ only in one amino acid in position 254 (Asp in chymosin A; Gly in chymosin B; Donnelly et al. 1984).…”

Genetic polymorphism of bovine chymosin

“…The existence, however, of individual calf variants has not been reported, and all previous studies of the enzyme have been carried out on protein of mixed animal origin. In a preliminary study (Donnelly et al 1984) we described the extraction of chymosin from four single stomachs, each of which contained two chromatographically distinct forms of the enzyme. We now report the identification of a chymosin/prochymosin variant, which differs from the A and B forms and apparently represents a third allele of the chymosin gene.…”

Natural heterogeneity of chymosin and pepsin in extracts of bovine stomachs

“…The two major chymosins A and B have been fully characterised including analysis of amino acid and gene sequences (Foltmann, Pedersen, Kauffman, & Wybrandt, 1979;Foltmann, 1992). It is generally agreed that chymosin A and B are allelic variants of a single gene locus (Donnelly, O'Callaghan, & Carroll, 1984), which differs by only one amino acid: the A form has an Asp in position 244 (according to the natural numbering of the chymosin sequence) where chymosin B has a Gly. There has been more doubt about chymosin C. Several papers (Foltmann, 1964;Foltmann, Pedersen, Jacobsen, Kauffman, & Wybrandt, 1977) conclude that chymosin C originates, at least partly, from autolytic degradation of chymosin A and Danley and Geoghegan (1988) describe the mechanism behind the formation of chymosin C. Donnelly, Carroll, O'Callaghan, and Walls (1986) have, however proposed, based on the extraction of a few single stomachs, that a third allelic chymosin exists.…”