Structure of asymmetric non-precipitating antibody: presence of a carbohydrate residue in only one Fab region of the molecule.

ABSTRACT

The reactions between purified precipitating and non-precipitating anti-DNP sheep and rabbit antibodies and the antigens DNP-BSA and DNP-GABA-BSA have been studied by immunodiffusion, complement fixation and an inhibition test. Both antigens reacted identically with precipitating antibodies. On the contrary, non-precipitating antibodies did not precipitate and did not fix complement with DNP-BSA but were able to do so with DNP-GABA-BSA. A different behaviour with both antigens was also demonstrated by an inhibition test. The properties of these antibodies were also studied after treatment with endo-beta-N-acetylglucosaminidase H. Non-precipitating antibody was able to give precipitin bands in gel diffusion and to fix complement with DNP-BSA after treatment with the enzyme. The treated antibody was able to agglutinate sensitized erythrocytes. Studies by fluorescence quenching showed that the affinity for the ligand DNP-GABA was significantly increased after hydrolysis of the carbohydrate residue. The properties of precipitating antibody were not modified by the endoglycosidase. Affinity chromatography of the F(ab')2 and Fab fragments obtained from precipitating and non-precipitating antibodies was made with Con A-Sepharose. The Con A retained all the F(ab')2 and 50% of the Fab from non-precipitating antibody, which were subsequently eluted with alpha-methyl-D-mannoside. The fragments from precipitating antibody were not retained at all. It is concluded that the asymmetry of the non-precipitating antibody molecule is due to a carbohydrate moiety which is present in only one of the Fab regions. This carbohydrate affects the reaction between the combining site and the antigen, and renders the molecule functionally univalent.