Subcellular distribution of glycolyltransferases in rodent liver and their significance in special reference to the synthesis of N-glycolyneuraminic acid.

The enzymic synthesis, transfer, and utilization of glycolyl-CoA (i.e. 2-hydroxyacetyl-CoA) have been studied in rat and mouse livers. On the one hand, these tissues contain the enzyme activities allowing the synthesis of glycolyl-CoA from fatty acids (palmitate omega-hydroxylase, omega-hydroxypalmitoyl-CoA synthetase, and mitochondrial beta-oxidation of omega-hydroxypalmitoyl-CoA) and 3-hydroxypyruvic acid (oxidation by intact mitochondria). On the other hand, three types of glycolyltransferase activities can be demonstrated in rodent livers, depending on either carnitine, glucosamine, or glucosamine-6-phosphate. The subcellular distributions of these glycolyltransferase activities are similar to those of the corresponding acetyltransferase counterparts. Concerning carnitine glycolytransferase, the activity is widely distributed in the subcellular fractions, pointing out its occurrence in most cell compartments. By contrast, the glucosamine and glucosamine-6-phosphate glycolytransferase activities were located preferentially in the microsomal fraction. The condensation between glycolyl-CoA and glucosamine (or glucosamine-6-phosphate) raises the interesting question of the nature and the role of the resulting glycolylglucosamine molecule, especially in an alternative N-glycolylneuraminic acid synthesis pathway.