Chymosin is synthesized in the mucosa of the abomasum (fourth stomach) of young (unweaned) ruminants. The enzyme hydrolyzes casein to paracasein. Broad specificity similar to that of pepsin A. Clots milk by cleavage of a single 104-Ser-Phe-|-Met-Ala-107 bond in kappa-chain of casein. Monomer. Forms A and B are probably allelic variants. Form B is the predominant form and differs only in one position. Belongs to the peptidase A1 family.