Chymosin: a short review on foetal and neonatal gastric proteases

All vertebrates in which the age dependent expression of gastric proteases has been investigated show a characteristic developmental pattern. Neonatal proteases which show partial immunochemical identity with calf chymosin have been observed in several species. The amino acid sequence of lamb chymosin shows 94% of identity with that of calf chymosin. Chymosins from pig and cat show about 85% and 75% of identity with calf chymosin. Chicken embryonic pepsinogen appears to be more related to calf chymosin than to other gastric proteases. A pseudo-gene for a chymosin-like protease from man has been identified. But a functional, human chymosin-like neonatal protease has not been identified. The possible physiological significance of chymosin and the clotting of milk are discussed.