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 pr otein kinase and lipid kinase activities of preparations of human secretory immunoglobulin A (sIgA) has been studied. The preparations of sIgA were is olated from human milk by chromatography on the column with Protein A-Sepha rose and DEAE-sorbent (sIgA1), by affinity chromatography of sIgA1 on DNA-c ellulose (sIgA2), and by gel-filtration of sIgA1 in buffer containing 5% di oxane (sIgA3). Two P-32-labeled products with high and low electrophoretic mobility in polyacrylamide gel containing SDS were found after incubation o f sIgA1 and sIgA2 with [gamma-P-32]ATP. The product with low electrophoreti c mobility was degraded in 10% trichloroacetic acid giving a radioactive ba ckground in lanes of the polyacrylamide gel. P-32-Labeled phospholipids wer e found among the phosphorylation products. Soluble and immobilized DNA inc rease lipid kinase activity of preparations of sIgA. In this case the secre tory component and H-chains of sIgA were degraded. Fractions possessing lip id kinase activity were precipitated in the presence of heparin (1 mg/ml), and lipid kinase activity was separated from sIgA by gel-filtration in buff er containing 5% dioxane. P-32-Labeled products were formed in the presence of [gamma-P-32]ATP as well as [P-32]ortho-phosphoric acid. The influence o f heparin and synthetic deoxy- and ribooligonucleotides on casein kinase ac tivity of sIgA3 was studied. It was observed that deoxyribooligonucleotides in micromolar concentrations increased casein phosphorylation in the prese nce of sIgA3 and [gamma-P-32]ATP. It has been proposed that catalytically a ctive sIgA have an affinity to DNA (anti-DNA sIgA) and can be present in hu man milk as a part of lipoprotein complexes.