The distribution of protein-bound carbohydrates in submicrosomal fractions from rat liver

Abstract

1. 1. Subfractions of washed rough and smooth microsomes were prepared by sonication and deoxycholate treatment. The amount of protein-bound mannose, galactose, glucosamine and sialic acid (NANA) in the subfractions has been determined. 2. 2. The vesicle protein obtained from rough and smooth microsomes contained the same amounts of mannose, whereas the galactose and glucosamine content was significantly larger in the vesicle protein from smooth microsomes. The Gal smooth vesicles/Gal rough vesicles ratio was 3.3, and GlcN smooth vesicles/GlcN rough vesicles ratio was 1.9. Sialic acid was found only in the smooth vesicle protein. The results support the “multi-site” hypothesis for attachment of carbohydrate to the polypeptide chain. 3. 3. Mannose and glucosamine were found in similar amounts in total protein from rough and smooth membranes. The Gal smooth membranes/Gal rough membranes ratio was 3.3, and the NANA smooth membranes/NANA rough membranes ratio was 2.7. 4. 4. The amino acid composition and the disc electrophoretic pattern of the vesicle proteins from rough and smooth microsomes were similar. A high degree of similarity in amino acid composition and the disc electrophoretic pattern was also found for the membrane proteins from rough and smooth microsomes, although different from that obtained for the vesicle protein.