Membrane glycoprotein transferases: Time courses of activity changes in a synchronized cell population and enzyme activity half-lives in an asynchronous population

The time course of activity changes of five membrane glycoprotein transferases: the glycoprotein:galactosyl, the fetuin:fucosyl, the PSM:fucosyl, the fetuin:N-acetylglucosaminyl, and the polypeptide: N-acetylgalactosaminyl was determined using defined acceptors and conditions in synchronized L5178Y cells. In addition, time course of activity changes of these transferases was determined for the endogenous acceptors present in the cell extract. Each of the membrane glycoprotein transferases was an S peak enzyme in the L5178Y cell. Activity with endogenous acceptors, in general, was constant throughout the cell cycle indicating that acceptor availability may, in part, control glycoprotein synthesis in vivo.