Peptide substrates for chymosin (rennin). Interaction sites in k-casein-related sequences located outside the (103-108)-hexapeptide region that fits into the enzyme's active-site cleft

The role of individual amino acid residues in the 98-102 and 111-112 regions of bovine k-casein in its interaction with the milk-clotting enzyme chymosin (rennin) was investigated. A model of the enzyme-substrate complex is proposed. Herein the 103-108 fragment of the substrate, to be accommodated within the enzyme's active-site cleft, is brought into position by electrostatic binding (via His-98, His-100, His-102 and Lys-111) near the entrance of the cleft.