The sialic acids. XVIII. Subcellular distribution of seven glycosyltransferases in embryonic chicken brain.

The subcellular distribution of seven glycosyltransferases was studied in embryonic chicken brain. Four of the transferases are required for the synthesis of gangliosides, and three for the synthesis of the terminal trisaccharide units of serum type glycoproteins. Six of the transferases were found only in the particulate fraction of homogenates, while one (UDP-galactose:glycoprotein galactosyltransferase) was found both in the paritculate and soluble fractions of young embryonic chicken brain, but only in the particulate fraction obtained from older embryos. The source of the soluble galactosyltransferase was found to be the fluid surrounding the embryonic brain. Fractionation studies by the Whittaker technique showed that the seven activities were located primarily in the nerve ending (synaptosome)-rich fraction.