Carbohydrate-binding Protein 35: Identification of the Galactose-specific Lectin in Various Tissues of Mice

In previous studies, a lectin designated as carbohydrate-binding protein 35 (CBP35) has been isolated from cultured mouse 3T3 fibroblasts. In this study, antibodies directed against CBP35 were used to screen for cross-reactive proteins in various cultured cells and in various organs and tissues of mice. Cross-reactive proteins of the same molecular weight (Mr, 35,000) were found in human, mouse, and chicken fibroblasts and in a macrophage-like cell line, P388D1. Similarly, cross-reactive proteins were also found in the embryonic liver, lung, spleen, thymus, skin, and muscle tissue and in the lung, artery, thymus, and spleen of the adult mouse. Fractionation of extracts of mouse lung on affinity columns of asialofetuin-Sepharose yielded a protein whose molecular weight, carbohydrate-binding specificity, and immunological properties suggest that it is CBP35 derived from the lung, hereafter designated CBP35 (lung). The binding of 125I-labeled CBP35 (lung) to rabbit erythrocytes was quantitated in the presence and absence of various carbohydrates. It was found that only carbohydrates containing galactose were inhibitors of the binding; the disaccharide lactose was 100-fold more potent as an inhibitor than was the monosaccharide galactose. When extracts of the adult mouse liver were fractionated by asialofetuin-Sepharose chromatography, only a protein corresponding to CBP16 was isolated; no CBP35 was found. These results corroborate the immunoblotting data, which indicated that CBP35 was not detectable in the adult mouse liver.