Chymosin (or rennin, not to be confused with renin, a kidney hormone) is an aspartic acid protease enzyme found in rennet. It is produced by the cow, in the lining of the abomasum (the fourth, final, chamber of its stomach). Bovine chymosin is produced nowadays recombinantly in, Aspergillus niger var awamori, and as alternative resource to the one from the cows. The gene is found in humans (on chromosome 1), but it isn't in a functioning form. Rennin is produced by gastric chief cells in infant… (More on Rennin)