Chymosin is synthesized in the mucosa of the abomasum (fourth stomach) of young (unweaned) ruminants (PubMed:16488399). The enzyme hydrolyzes casein to paracasein (PubMed:16488399, PubMed:23633601, PubMed:25726113, PubMed:25837439). 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. kcat is 5.1 sec(-1) for undecapeptide analog to chymosin sensitive region of camel kappa-chain of casein and kcat is 11.7 sec(-1) for undecapeptide analog to chymosin sensitive region of bovine kappa-chain of casein (PubMed:16488399). Activity is 462 International Milk-Clotting Units (IMCU) per mg enzyme. kcat is 11 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (unglycosylated form of chymosin at pH 6.7), kcat is 53 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (unglycosylated form of chymosin at pH 6.0), kcat is 47 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (unglycosylated form of chymosin at pH 5.5), kcat is 14 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (double-glycosylated form of chymosin at pH 6.7), kcat is 65 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (double-glycosylated form of chymosin at pH 6.0) and kcat is 59 sec(-1) for a labeled peptide substrate of 98-112 of bovine kappa-chain of casein (double-glycosylated form of chymosin at pH 5.5) (PubMed:25726113). Activity is 400 IMCU per ml enzyme. Supplemental CaCl(2) at concentration between 20-40 mM is optimal for stable enzyme activity (PubMed:25837439). Optimum pH is about 5.1 (PubMed:16488399). Activity decreases with increasing pH values (PubMed:25837439). Optimum temperature is between 45-55 degrees Celsius (PubMed:16488399, PubMed:25837439). 50% activity at 35 and 60 degrees Celsius. No activity below 20 or above 70 degrees Celsius (PubMed:25837439). The extraordinary high clotting activity, combined with its very low non-specific activity may be useful in the production of cheese types, for which a bitter taste is unfavorable, for example Mascarpone type cheese (PubMed:16488399). Large-scale expression of camel chymosin gene in P.pastoris could represent an excellent system for producing active chymosin for potential use in the commercial production of cheese (PubMed:25837439). Belongs to the peptidase A1 family.