Influence of nucleic acids and polysaccharides on phosphotransferase activity of preparations of secretory immunoglobulin A from human milk

The influence of nucleic acids (DNA, tRNA), synthetic oligonucleotides, and polysaccharides (lipopolysaccharides from Escherichia coli, heparin) on protein kinase and lipid kinase activities of preparations of human secretory immunoglobulin A (sIgA) has been studied. The preparations of sIgA were isolated from human milk by chromatography on the column with Protein A-Sepharose and DEAE-sorbent (sIgA1), by affinity chromatography of sIgA1 on DNA-cellulose (sIgA2), and by gel-filtration of sIgA1 in buffer containing 5% dioxane (sIgA3). Two 32P-labeled products with high and low electrophoretic mobility in polyacrylamide gel containing SDS were found after incubation of sIgA1 and sIgA2 with gamma-32P]ATP. The product with low electrophoretic mobility was degraded in 10% trichloroacetic acid giving a radioactive background in lanes of the polyacrylamide gel. 32P-Labeled phospholipids were found among the phosphorylation products. Soluble and immobilized DNA increase lipid kinase activity of preparations of sIgA. In this case the secretory component and H-chains of sIgA were degraded. Fractions possessing lipid kinase activity were precipitated in the presence of heparin (1 mg/ml), and lipid kinase activity was separated from sIgA by gel-filtration in buffer containing 5% dioxane. 32P-Labeled products were formed in the presence of gamma-32P]ATP as well as 32P]ortho-phosphoric acid. The influence of heparin and synthetic deoxy- and ribooligonucleotides on casein kinase activity of sIgA3 was studied. It was observed that deoxyribooligonucleotides in micromolar concentrations increased the rate of casein phosphorylation in the presence of sIgA3 and gamma-32P]ATP. It has been proposed that catalytically active sIgA have an affinity to DNA (anti-DNA sIgA) and can be present in human milk as a part of lipoprotein complexes.