Amylolytic activity of IgG and sIgA immunoglobulins from human milk

Background: New natural amylolytic abzymes (Abs) for catalytically active antibodies from human milk have been identified and investigated. Methods: The amylolytic activity of human milk autoantibodies was studied by TLC and HPLC techniques analyzing the hydrolysis of maltooligosaccharides with different degrees of polymerization and of 4-nitrophenyl 4,6- O-ethylidene-α- d-maltoheptaoside (EPS). IgG and sIgA fractions were isolated from human milk by affinity chromatography. After SDS-PAGE preparation of native IgG and sIgA and their renaturation, the amylolytic activity was in-gel assayed. Results: All electrophoretically homogeneous preparations of IgG and its Fab fragments as well as sIgA antibodies possessed α-amylolytic activity. The specific activities of these catalytic antibodies varied in the range from 1.83 up to 3.33 kat/kg, which is about one order of magnitude higher than that for IgGs from the sera of cancer patients. IgG and sIgA fractions showed Michaelis constants for hydrolysis of 4-nitrophenyl 4,6- O-ethylidene-α- d-maltoheptaoside in the range of 10 −4 M/l. Fractions of autoantibodies from different donors exhibited different modes of action in hydrolysis of maltooligosaccharides, maltose and p-nitrophenyl-α- d-glucopyranose. Conclusions: IgG antibodies, their Fab fragments, and sIgA fractions isolated from human milk of healthy women possessed amylolytic activity in the hydrolysis of maltooligosaccharides and several artificial substrates.