title: Caseins are cross-linked through their ester phosphate groups by colloidal calcium phosphate.
abstract: Artificial casein micelles were prepared by adding 30 mM calcium, 22 mM phosphate and 10 mM citrate to sodium caseinate solutions, and the content of the casein aggregates cross-linked by colloidal calcium phosphate was determined by high-performance gel chromatography on a TSK-GEL G4000SW column in the presence of 6 M urea. The content of the casein aggregates cross-linked by colloidal calcium phosphate in artificial whole casein micelles was 48% of total casein, and their relative casein composition determined by high-performance ion-exchange chromatography was 53.1% for alpha s1-casein, 15.8% for alpha s2-casein, 31.1% for beta-casein and 0% for kappa-casein. The order of cross-linking by colloidal calcium phosphate agreed with that of the ester phosphate content of casein constituents. The content of the casein aggregates cross-linked by colloidal calcium phosphate was higher in alpha s1-kappa-casein micelles than in beta-kappa-casein micelles. kappa- and gamma-caseins and dephosphorylated alpha s1-casein were not cross-linked by colloidal calcium phosphate. Although kappa-casein was not cross-linked, chemically phosphorylated kappa-casein, of which the average phosphate content was 8.5 per molecule, was cross-linked. It is concluded that caseins are cross-linked through their ester phosphate groups by colloidal calcium phosphate.
mesh_terms: D000818:Animals; D002118:Calcium; D002364:Caseins; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002951:Citrates; D003102:Colloids; D003432:Cross-Linking Reagents; D004952:Esters; D008823:Micelles; D010710:Phosphates
chemical_list: D002364:Caseins; D002951:Citrates; D003102:Colloids; D003432:Cross-Linking Reagents; D004952:Esters; D008823:Micelles; D010710:Phosphates; D002118:Calcium