Enzymatic studies on GM1 ganglioside biosynthesis

An enzyme that catalyzed the terminal step in GM(,1) ganglioside biosynthesis was demonstrated in rat brain and rat liver microsomal preparations. This galactosyltransferase enzyme could be solubilized from the Golgi fraction of rat liver homogenates. Anion exchange chromatography resolved two distinct enzymes with activity toward GM(,2) ganglioside. These two activities could be distinguished by such properties as pH optima, detergent requirements, and isoelectric points. The two enzymes had similar molecular weights and cation requirements.Extensive characterization of the acceptor specificities of galactosyltransferase enzymes present in solubilized Golgi preparations led to the identification of five enzyme reactions. Two activities were identified which had a requirement for acceptors within the glycoprotein family. A single activity supported the biosynthesis of GM(,1) ganglioside only. The fourth galactosyltransferase activity catalyzed the incorporation of galactose into both ganglioside and glycoprotein