Mechanism of cross-linking of casein by colloidal calcium phosphae in casein micelles

钙和无机磷的存在超过了它们的溶解度，并与酪蛋白相互作用。与酪蛋白有关的磷酸钙和酪蛋白胶束称为胶体磷酸钙(CCP)。虽然CCP通过磷酸基团使酪蛋白发生交联化，但其交联剂的作用机理尚未完全阐明。在本研究中，从人工合成的人酪蛋白胶束中分离出少量的人β-酪蛋白的3-P组分，以及相当数量的4-P和5-P组分。人β-酪蛋白的3-P和4-P组分与kappa-酪蛋白在人工酪蛋白胶束中形成CCP-交联型酪蛋白。相反，1-P和2-P人工酪蛋白胶束中没有形成交联线。结果表明，在酪蛋白钠溶液中加入钙、磷和柠檬酸盐后，CCP.CCP交联型酪蛋白至少需要3个磷酸基团进行FGR交联。当α-酪蛋白的氨基被乙酰化、柠檬酰化或琥珀酸化后，修饰的α-酪蛋白与天然酪蛋白相比几乎不会被CCP交联。

Calcium and inorganic phosphate are present in excess of their Solubility and interact with casein. Calcium phosphate ity casein micelles, which is associated with casein, is called colloidal calcium phosphate(CCP). Although CCP cross-links caseins through phosphate groups, the mechanism of cross-linking has not yet been elucidated sufficiently. In the present study following results were obtained.A small amount of the 3-P component of human beta-casein and a considerable amount of the 4-P and 5-P components were found in the CCPcross-linked casein separated from artificial casein micelles of whole human casein. CCP-cross-linked casein was formed in artificial casein micelles of tlie 3-P and 4-P components of human beta-casein with kappa-casein. In contrast, no cross-linitage was formed in artificial casein micelles of the 1-P and 2-P coutponeiits. It was concluded that at least three phosphate groups were need fGr cross-linking of casein by CCP.CCP-cross-linked casein taras formed when calcium, phosphate and citrate were added to sodium caseinate solution. This suggested that the submicelle structure and ordered structures of casein were unnecessary for caseins to be cross-linked by CCP.When amino groups of alpha_<s1>-casein were acetylated, citraconilated, orsuccinylated, modified alpha_<s1>-casein was somewhat more hardly cross-linked by CCP than native one.Egg white ribofravin-binding protein is also cross-linked through its phosphate groups by CCP.