Purification and partial characterization of milk clotting proteases from flowers of Cynara cardunculus

Three proteases (cynarases 1, 2 and 3) with milk-clotting activity have been purified from dried flowers of Cynara cardunculus. The proteases are each composed of one large and one small subunit. The native M r of the dimeric proteins is 49 000. The three proteases are glycoproteins containing N-linked high mannose type glycans. Cynarase 3 shows the highest proteolytic and milk-clotting activity. All three enzymes express maximum activity at pH 5.1. Inhibitor studies indicate that the cynarases are of the aspartic acid type. Antibodies raised against the large subunit of cynarase 3 cross-reacts with the large subunits of the other two cynarases after destruction of the glycan structure by periodate oxidation.