Galactosyl transferase of a Golgi fraction from cultured neoplastic mast cells.

Abstract

Suspension cultures of neoplastic mouse mast cells were used to obtain large quantities of a homogeneous cell population as starting material for cell fractionation. A Golgi fraction was prepared by slight modification of established techniques and identified by EM. Assay of galactosyl transferase activity using ovalbumin, desialylated degalactosylated orosomucoid, and N-acetylglucosamine as galactose acceptors showed that the Golgi fraction was enriched in specific activity over the homogenate. The Golgi galactosyl tranferase was examined in detail. Acceptor concentrations for optimal galactose incorporation were determined, and substrate inhibition effects were shown with higher concentrations of all 3 acceptors. Mn was necessary for galactose incorporation. A higher concentration of Mn afforded some protection from substrate inhibition by acceptors, but at the same time was itself inhibitory. All 3 acceptors competed with one another for galactose incorporation, indicating that 1 enzyme catalyzed the transfer of galactose for all acceptors.