The Least Number of Phosphate Groups for Crosslinking of Casein by Colloidal Calcium Phosphate

Abstract

Artificial casein micelles were formed with whole human casein at 20mM calcium, 17mM phosphate, and 10mM citrate. The casein micelles disaggregated by 6 M urea were separated by high performance gel chromatography on a TSK-GEL G4000SW column into crosslinked and monomeric fractions. When the crosslinked casein fraction was analyzed by high performance ion-exchange chromatography on a TSK-GEL DEAE-5PW column, a small peak, representing the 3-P component of human β-casein, and distinct peaks of the 4-P and 5-P components were found. Artificial casein micelles were formed from mixtures of each purified component of human β-casein and bovine κ-casein, disaggregated by urea, and separated on a TSK-GEL G4000SW column. The casein aggregates crosslinked by colloidal calcium phosphate were formed in artificial casein micelles of the 3-P and 4-P components. In contrast, no crosslinkage was formed in artificial micelles of the 1-P and 2-P components. The results indicate that at least three phosphate groups are needed for crosslinking of casein by colloidal calcium phosphate.