Distribution of plasminogen activator in different fractions of bovine milk

Abstract

SUMMARYThe 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.

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

“…Raw milk batches were homogenized and pasteurized under the same conditions to eliminate any effects on plasmin activity. Indeed, disruption of somatic cells upon processing can improve plasmin activity by releasing intracellular activators of plasminogen (Heegaard et al, 1994;White et al, 1995). Moreover, time/temperature conditions of pasteurization could differently increase plasmin activity by inactivating native inhibitors of plasminogen-converting compounds.…”

Polymorphonuclear neutrophils and Escherichia coli proteases involved in proteolysis of casein during experimental E. coli mastitis

“…Indeed, the commercial plasmin was obtained by adding this serine protease to plasminogen. The uPA, which is present in bovine milk, is the predominant form of plasminogen activator associated with somatic cells (White et al, 1995). Urokinase activity has been associated with $30 and $50 kDa bands on SDS-PAGE under non-reducing conditions.…”

Effect of heat treatment on the activity of inhibitors of plasmin and plasminogen activators in milk

“…The activity of PL or PAs may be inhibited by plasmin inhibitors (PIs) or plasminogen activator inhibitors (PAIs), respectively (Precetti, Oria, & Nielsen, 1997). Unlike PL, PG, and PAs, which associate with casein micelles (Baer, Ryba, & Collin, 1994;Grufferty & Fox, 1988;Haissat et al, 1994;Politis, Barbano, & Gorewit, 1992;White et al, 1995), the inhibitors are found in the serum fraction of fluid milk (Reimerdes, Klostermeyer, & Sayk, 1976).…”