PROTEOLYSIS IN SAMPLES OF QUARTER MILK WITH VARYING SOMATIC-CELL COUNTS .2. COMPONENT PP3 AND BETA-CASEIN-1P (F29-105 AND F29-107) OF THE PROTEOSE-PEPTONE FRACTION

The proteose-peptone fraction was studied to measure proteolysis in 86 samples of quarter milk from 31 cows with subclinical mastitis. The r elative content of component PP3 decreased significantly in the total of proteose-peptone as plasmin activity increased, but the content of this component in milk was not correctly correlated with the plasmin a ctivity (r = .52). Electrophoresis, amino acid composition, and sequen ce analysis showed that the component beta-CN-1P (f29-105/7) of the pr oteose-peptone fraction was a terminal product of plasmin-like activit y and was located correctly electrophoretically. Correlation factors b etween the plasmin activity and content in milk of component beta-CN-1 P (f29-105/7) was very high (r = .87). This component could be used as indicator of the endogenous proteolysis in milk from cows with subcli nical mastitis.