Hydrolysis of Caprine β-Casein by Plasmin

Abstract

The proteolytic activity of plasmin on soluble caprine beta-casein (CN) was studied in 50 mM Tris.HCI buffer, pH 8.0, at 37 degrees C. Electrophoretic studies showed that hydrolysis of this protein results in an electrophoretic pattern that is similar to the pattern obtained from plasmin hydrolysis of bovine beta-CN (gamma-CN and complementary N-terminal fragments), suggesting that plasmin probably attacks the same regions that are susceptible to cleavage in bovine beta-CN. As determined by SDS-PAGE, the gamma-like components of caprine milk consisted of two fragments with relative molecular mass of 9200 and two with relative molecular mass of 21,400 that could differ in the level of phosphorylation. Apparently, the high molecular mass components are homologous to bovine beta-CN (f 29-209) (gamma 1-CN), and the low molecular mass components are homologous to bovine beta-CN (f 106-209) and beta-CN (f 108-209) (gamma 2- and gamma 3-CN). Complementary N-terminal fragments had values for molecular masses in the range 13,600 to 8500 and urea-PAGE patterns that were more complex than those obtained in bovine casein because of the different phosphorylation levels in caprine beta-CN. These fragments were also present in the hydrolysate of whole caprine casein that had been treated with plasmin.

An investigation of the plasmin–plasminogen system in caprine milk and cheese

“…3), which enabled evaluation of the b-and g-casein content by densitometry. As shown in Table 1, rennet curds showed higher relative contents of g-caseins than the acid curds, confirming the positive correlation between PL activity and the extent of b-casein hydrolysis (Trujillo et al, 1997).…”

“…In milk, PL is mainly associated with casein micelles, which are its substrate (Bastian & Brown, 1996). It is responsible for the hydrolysis of b-and a s2 -caseins (Aslam & Hurley, 1997;Trujillo, Guamis, & Carretero, 1997), cleaving mainly bonds of the type Lys-X and Arg-X. PL occurs in milk together with its inactive zymogen, plasminogen (PG).…”

Effect of partial or total substitution of bovine for caprine milk on the compositional, volatile, non-volatile and sensory characteristics of semi-hard cheeses

“…b-casein is the major casein in caprine milk and constitutes approximately 60% of the total casein. Its primary structure is similar to that of bovine b-casein in the regions that are susceptible to hydrolysis by plasmin (Trujillo et al, 1997a).…”

“…Furthermore, both caprine a s1 -casein and its primary breakdown product are more susceptible to rennet action than their bovine equivalents and the rate of proteolysis and the nature of breakdown products are pH dependent (Trujillo et al, 1997a(Trujillo et al, ,b, 1998.…”

Effect of microfiltration of milk on plasmin activity

“…PL (fibrinolysin, fibrinase, EC 3.4.21.7) is a blood enzyme that is found in milk with its inactive zymogen, plasminogen (PG), in a complex network involving activators and inhibitors of PL and PG in milk. PL readily hydrolyzes b-and a S2 -casein and shows slight activity against a S1 -casein (Aslam & Hurley, 1997;Crudden, Fox, & Kelly, 2005;McSweeney, Olson, Fox, Healy, & Højrup, 1993;Trujillo, Guamis, & Carretero, 1997). PL activity results in the formation of small peptides, including g-caseins and proteose peptones (Fox & McSweeney, 1998, p. 476), and is important for the ripening of different types of cheese (Barrett, Kelly, McSweeney, & Fox, 1999;Bastian, Hansen, & Brown, 1991;Bastian et al, 1997).…”