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Association of lipases with micellar and soluble casein complexes

Published online by Cambridge University Press:  01 June 2009

W. K. Downey  and
R. F. Murphy
W. K. Downey
Affiliation:
National Dairying Research Centre, The Agricultural Institute, Fermoy, Co. Cork, Irish Republic
R. F. Murphy
Affiliation:
National Dairying Research Centre, The Agricultural Institute, Fermoy, Co. Cork, Irish Republic
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Summary

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 > 108 whereas the casein in colloidal phosphate-free milk is present as soluble complexes of molecular weight ca. 2×106 containing αs-, β- and κ-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.

Type
Original Articles
Information
Journal of Dairy Research , Volume 37 , Issue 1 , February 1970 , pp. 47 - 59
Copyright
Copyright © Proprietors of Journal of Dairy Research 1970

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