Influence of Nucleic Acids and Polysaccharides on Phosphotransferase Activity of Preparations of Secretory Immunoglobulin A from Human Milk

Y. Y. Kit^*, D. V. Semenov, E. V. Kuligina, and V. A. Richter

Novosibirsk Institute of Bioorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, pr. Lavrent'eva 8, Novosibirsk, 630090 Russia; fax: (3832) 33-7677; E-mail: kit@niboch.nsc.ru

^* To whom correspondence should be addressed.

Received June 7, 1999; Revision received October 21, 1999

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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.

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KEY WORDS: human milk, abzymes, anti-DNA antibodies, polyanions, lipoproteins, phosphorylation

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