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Journal of Dairy Science Vol. 74 No. 7 2077-2081
© 1991 by American Dairy Science Association ®
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Properties of Proteases from Milk Somatic Cells and Blood Leukocytes

Robert J. Verdi 1 and David M. Barbano 1

1 Department of Food Science, Cornell University, Ithaca, NY 14853

Proteolytic activity of proteases associated with somatic cells isolated from high SCC milk and proteases associated with leukocytes isolated from bovine blood was assayed at pH 6.6 and 5.2 in a model system consisting of a ß-casein (.96%) substrate in Jenness/Koops buffer. Intact ß-casein and casein proteolysis products were measured by densitometric analysis of SDS-PAGE gels. Relative proteolytic activity was expressed as percentage degradation of ß-casein after 24 h at 37°C per 1 x 106 cells/ml. Proteolytic activity associated with somatic cells isolated from bovine milk was 27.5 and 13.6% at pH 6.6 and 5.2, respectively. Proteolytic activity associated with leukocytes isolated from bovine blood was 16.0 and 8.4% at pH 6.6 and 5.2, respectively. Proteolytic activity at pH 6.6 was significantly higher for the somatic cells isolated from milk than for leukocytes isolated from blood. The reason for the difference in proteolytic activity of leukocytes isolated from blood of a healthy cow versus somatic cells isolated from milk produced by a cow with mastitis is not known. Further work is needed to determine whether the difference may be caused by a higher proportion of activated macrophages in somatic cells isolated from milk produced by cows with mastitis than in the leukocytes isolated from blood of healthy cows.

Key Words: milk somatic cells • blood leukocytes • proteases

Submitted on September 11, 1989
Accepted on February 5, 1991




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