Effect of Bovine Plasmin on αs1 -B and κ-A Caseins

Abstract

Both .alpha.s1- and .kappa.-caseins were incubated at 37.degree. C in the presence of bovine plasmin (.28 mg/ml) prepared from fresh blood plasma. The electrophoretic pattern of .kappa.-casein A was unchanged following 60-min incubation with plasmin, but the electrophoretic band corresponding to .alpha.s1-casein B gradually disappeared during the initial 30-min incubation with plasmin. Proteolysis was accompanied by formation of 1 polypeptide band with electrophoretic mobility slightly slower than .alpha.s1-casein B and several bands with faster electrophoretic mobilities. Two of the faster electrophoretic bands contained phosphorus. Estimates of MW were 20,500, 12,300 and 10,300 daltons for 3 of these early degradation products of .alpha.s1-casein B by plasmin.