Distribution of plasminogen activator forms in fractions of goat milk

Distribution of plasminogen activator forms in fractions of goat milk was examined. Raw milk was centrifuged to separate skim milk, cream, and a somatic cell pellet. Somatic cell extracts were obtained by sonication. Skim milk was centrifuged to separate milk serum and casein micelles. Activity of plasminogen activator was detected in casein, serum fractions, and in association with somatic cells. Plasminogen activator forms in milk casein had approximate molecular weights of 75,000, 50,000, and 30,000. The predominant forms of plasminogen activator in milk serum and in association with milk somatic cells had molecular weights of 30,000 and 50,000. Based on fibrin dependency and inhibition of activity in the presence of amiloride, the forms at 30,000 and 50,000 represent urokinase-plasminogen activator, and the form at 75,000 represents tissue-plasminogen activator.