Introductory Remarks on Ganglioside Metabolism

Abstract

Most of sialylated glycolipids occur in nervous tissue. In extraneural tissues which have mostly non-sialylated glycolipids, the gangliosides constitute a relatively small fraction. Only little information is available on the metabolic sequences which result in biosynthesis, deposition and subsequent degradation of the ganglioside in neural membranes. Some attempts were made to measure ganglioside biosynthesis by injecting labelled precursor into animals. However, these have not provided sufficient information on the metabolic events occurring in vivo. This short review of ganglioside metabolism will be confined to the reactions which synthesise or degrade these compounds and the enzyme which catalyze them, namely the glycolipid transferases and hydrolases. Though strictly-defined as sialic acid-containing glycolipids, a discussion of the metabolism of gangliosides must also include metabolic sequences of ceramide and its mono- or oligohexosyl derivatives. Studies on these enzymes were begun in the 1960’s and in the last 15 years a considerable number of publications appeared. In this discussion the earlier work on the transferases and hydrolases will be reviewed and the reader will be directed to monographs which treat the more recent aspects of ganglioside metabolism in a comprehensive manner. The most updated discussion of enzymes of glycolipid metabolism is the book which summarizes the proceedings of the Meeting on Enzymes of Lipid Metabolism held at Mont Ste Odile exactly two years ago, only a short distance from the present meeting place (GATT, FREYSZ and MANDEL, 1978).