Temperature-dependent dissociation of human micellar 13-casein: Implications of its phosphorylation degrees and casein micelle structures

Temperature-dependent dissociation of human micellar 13-casein regarding its phosphorylation degrees and micelle structures were studied. Human milk was fractionated at 25 degrees C into soluble (S-25 degrees C) and micellar (M25 degrees C) fractions, and the latter was fractionated at 4 degrees C into soluble (S-4 degrees C) and micellar (M-4 degrees C) fractions. 13-casein ratios among S-25 degrees C, S-4 degrees C and M-4 degrees C were 19%, 59% and 22%. 13-casein isoforms were predominated by 0-P, 1-P and 2-P in S-25 degrees C, by 0-P, 1-P, 2-P and 4-P in S-4 degrees C, and by 0-P in M-4 degrees C. For micelles remained after dissociation of 13-casein and calcium, the size increased, molar mass decreased, morphologies were maintained, and internal protein inhomogeneities disappeared, compared with micelles in M-25 degrees C. 13-casein isoforms with lower phosphorylation degrees may form a frame mainly through hydrophobic interactions, attached with more highly phosphorylated isoforms and colloidal calcium phosphate via calcium bridges for forming human micelle.

Automated summary

The temperature-dependent dissociation of human micellar 13-casein and its phosphorylation degrees were studied. Lower phosphorylation degrees of 13-casein isoforms may form a frame through hydrophobic interactions, attached with more highly phosphorylated isoforms and colloidal calcium phosphate via calcium bridges for forming human micelles.