Immunochemical Specificities of the Combining Sites of Bovine Immunoglobulins Reactive with Sepharose 4B

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Binding specificities of calcium-dependent and -independent bovine IgM and IgG reactive with unsubstituted Sepharose 4B were determined by competitive binding assays. The binding of ¹²⁵I-labeled calcium-dependent bovine IgM to unsubstituted Sepharose 4B was most effectively inhibited by lactose which was about 100 times more reactive than galactose and melibiose. Other inhibitors were much less potent. With ¹²⁵I-labeled calcium-independent bovine IgM and IgG, on the other hand, lactose was as potent as galactose. Melibiose was about 10 times less potent than lactose and galactose, whereas other mono- and disaccharides were much less potent. From these findings, the combining site of calcium-dependent bovine IgM reactive with unsubstituted Sepharose 4B may be specific for lactose, whereas those of calcium-independent bovine IgM and IgG specific for galactose.