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Distribution of plasminogen activator in different fractions of bovine milk

Published online by Cambridge University Press:  01 June 2009

Jeffrey H. White
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
Boris Zavizion
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
Kristen O'Hare
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
James Gilmore
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
Ming R. Guo
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
Paul Kindstedt
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA
Ioannis Politis
Affiliation:
Department of Animal and Food Sciences, University of Vermont, Burlington, VT 05405, USA

Summary

The type and relative amounts of plasminogen activator (PA) in different fractions of bovine milk obtained from 15 Holstein cows were examined. Raw milk was centrifuged to separate skim milk and a somatic cell pellet. PA was mainly localized within the casein fraction, being 42 times that in the serum, and in association with somatic cells. The predominant form of PA in milk casein was isolated from SDS-PAGE gel extracts and had a molecular mass of ∽75 kDa. Its activity was increased 41-fold (P < 0·01) in the presence of fibrin but was unaffected by the presence of amiloride, indicating that it was due to tissue-PA. The predominant forms of PA associated with milk somatic cells were isolated from SDS-PAGE gel extracts and had molecular masses of ∽ 30 and ∽ 50 kDa. The activity of both proteins was unaffected by the presence of fibrin but was dramatically reduced by the presence of amiloride, indicating that they represented urokinase-PA.

Type
Original articles
Copyright
Copyright © Proprietors of Journal of Dairy Research 1995

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