Different half-lives of the carbohydrate and protein moieties of a 110,000-dalton glycoprotein isolated from plasma membranes of rat liver.

Abstract

By using a 4-step procedure (solubilization with Triton X-100, affinity chromatography on concanavalin A-Sepharose, affinity chromatography on wheat germ lectin-Sepharose, preparative sodium dodecyl sulfate gel electrophorphoresis) a glycoprotein was isolated from rat liver plasma membrane. MW is 110,000 and the isoelectric point is 5.8. It contains L-fucose, N-acetylneuraminic acid, D-galactose, D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine and considerable quantities of aspartate, threonine, serine and leucine. In pulse-chase experiments the half-lives of methionine and arginine, representing the half-life of the protein, were determined as 70 h and 78 h, respectively. Half-lives of the terminal carbohydrates L-fucose and N-acetylineuraminic acid were 12.5 and 33 h, respectively. The galactose half-life was 20 h. Terminal sugars turn over several times in the life-span of this protein molecule. This process may be operative during membrane recycling mechanisms.