Action on bovine alpha S1-casein of cardosins A and B, aspartic proteinases from the flowers of the cardoon Cynara cardunculus L
1996
Ramalho-Santos, M. | Verissimo, P. | Faro, C. | Pires, E.
The cleavage of purified bovine alpha S1-casein separately by cardosin A and cardosin B, two distinct milk-clotting aspartic proteinases (APB) present in the stigmas of the plant Cynara cardunculus L., was studied. Casein digestion peptides were separated either by SDS-PAGE or by reverse-phase HPLC, and their N-terminal amino-acid sequences were subsequently determined by automated Edman degradation, thus identifying the cleavage sites. Results showed that both enzymes exert a similar but distinct action on bovine alpha S1-casein. In common they have the preference for the bond Phe23-Phe24, and the cleavage of Trp164-Tyr165 and Phe153-Tyr154. Cardosin A also cleaves the bond Tyr165-Tyr166, whereas Cardosin B cleaves an extra type of bond, Phe150-Arg151, revealing a slightly broader specificity. A model for the action of both enzymes on bovine alpha S1-casein is proposed and discussed. In comparison with the reported action of chymosin on bovine alpha S1-casein, both cardosins proved to have a broader specificity towards this particular substrate due to a higher ability to cleave bonds between residues with large hydrophobic side-chains.
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