Association of lipases with micellar and soluble casein complexes

Abstract

The association of lipase with casein micelles and soluble casein complexes was investigated by gel-filtration on Sephadex G-200 and Sepharose 2B columns which were equilibrated with synthetic milk serum. Gel-filtration indicated that the molecular weight of casein micelles in milk is > 10 8 whereas the casein in colloidal phosphate-free milk is present as soluble complexes of molecular weight ca. 2 x 10 6 containing as-, ft-and /c-casein. The soluble complexes appear to be stabilized in the micelle by colloidal calcium phosphate linkages. On addition of pancreatic lipase to milk, activity was impaired due to binding of the enzyme both to micellar and to soluble casein complexes. The enzyme dissociated from the latter during gel-filtration on Sepharose 2B columns. The binding of lipase to casein was not dependent on the presence of colloidal phosphate and consequently complete micellar structure is not essential for association of lipase with casein. Binding of the lipase to phosvitin did not result in a loss of enzyme activity. Lipases in milk appear to be involved in the equilibrium between micellar and soluble casein. The activity of lipases in milk is apparently influenced by this equilibrium. Some problems encountered in the use of gel-filtration to study the interactions of lipases with caseins are described.

Pulmonary Vascular Effects of Amrinone in Conscious Lambs

“…Amrinone is a nonglywside, noncatechole cardiac inotropic agent, which is currently used in the therapy of chronic congestive heart failure in adults (3,4,12,13,14,18,19). Its inotropic effects have been established in isolated muscle preparations (2,8), intact animals (1,2, 8), and in humans (3,6,11).…”

“…Studies on the effect of such antibohy in hum& infants have ihown suppression or enhancement of antibody formation to parenteral application of diphtheria toxoid (4,13), whereas the response to oral polio vaccine was not affected by either circulating or secretory antibody of the mother (10). No effect of passive antibody on the immune response to BSA was seen in adult rabbits (18).…”

Lipolysis and the distribution of lipase activity in bovine milk in relation to stage of lactation and time of milking

“…Lipolysis in bovine milk is influenced by a variety of factors (Jellema, 1975;Olivecrona, 1980) but it is generally accepted that the free fatty acid (FFA) concentration is poorly correlated with milk lipase activity (Castberg & Solberg, 1974). Much of the lipase activity in bovine milk is associated with micellar casein (Downey & Murphy, 1970) in fresh uncooled milk. However, cooling (Wang & Randolph, 1978), addition of NaCl (Downey & Andrews, 1966) or heparin (Hoynes & Downey, 1973) cause redistribution of the enzyme.…”

Relationship of the Lipase and Lipoprotein Lipase Activities of Bovine Milk

“…lb, l c and Id) the lipolytic activities against the two substrates are distributed between the casein micelles (mol.wt. >lo8; Downey & Murphy, 1970) and the soluble casein complexes (mol.wt. 0.5 x lo6), and alteration of the concentration of heparin induces a comparable shift in the distribution of the two lipolytic activities between the micellar and soluble casein complexes.…”