PHOSPHORYLATION OF DIFFERENT HUMAN-MILK PROTEINS BY HUMAN CATALYTIC SECRETORY IMMUNOGLOBULIN-A

The ability of secretory immunoglobulin A (slgA) from milk of healthy mothers to phosphorylate various milk proteins in the presence of gamm a-[P-32]-ATP was shown to be a property of the antibodies. The polyclo nal slgA was purified by sequential chromatography on Protein-A Sephar ose and DEAE-cellulose, and then separated by chromatography on the AT P-Sepharose. The preparations containing all milk proteins except for protein kinases [integrated milk proteins (IMP)] were obtained by extr action of the kinase activities from the milk using their affinity to the insoluble crosslinked staphylococcus. Addition of slgA fractions ( having a different affinity to ATP) to the IMP led to phosphorylation of casein and several other milk proteins with different efficiencies.