Characterization and proteolytic origins of specific peptides appearing during lipopolysaccharide experimental mastitis.

Based on the compositional change of the proteose peptone fraction, proteolysis was studied over time following lipopolysaccharide-induced experimental mastitis. Electrophoresis of the proteose peptone fraction revealed many degradation products. Five peptides were identified by amino-terminal sequencing as internal fragments of beta-, kappa-, alpha(s1)-, and alpha(s2)-casein that were generated by somatic cell proteases. Although kappa-casein is considered particularly resistant to endogenous proteolysis, a kappa-casein peptide was electrophoretically isolated in association with a beta-casein fragment. The in vitro kinetic studies of caseinate hydrolysis by elastase, one of the main polymorphonuclear neutrophil (PMN) proteases, suggested that the beta-casein peptide might be generated by elastase. In addition, elastase activity in milk PMN was higher during the inflammation of the mammary gland than prior to infusion.