This paper describes the kinetic properties of three glycosyltransferases found in the synaptosome-rich fraction obtained from embryonic chicken brain: CMP-N-acetylneuraminic acid:glycoprotein sialyltransferase; UDP-galactose:glycoprotein galactosyltransferase; and UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase. These enzymes synthesize the terminal trisaccharide, sialyl → galactosyl → N-acetylglucosaminyl, of serum type glycoproteins by stepwise addition of the respective glycose moieties. Three other galactosyltransferase activities were detected in the same fraction. These catalyze transfer of the galactosyl group to the terminal N-acetylgalactosaminyl residues of sialidase-treated mucins, to Tay-Sachs ganglioside, and to xylosylserine. A distinguishing characteristic of all of the particulate enzymes is their absolute requirement for detergent for activity. At early stages of development, UDP-galactose:glycoprotein galactosyltransferase and UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase were found in soluble form in the fluid surrounding embryonic chicken brains. The soluble galactosyltransferase was also detected in embryonic and adult chicken serum, amniotic fluid, and vitreous humor, and in human spinal fluid. The possible significance of this enzyme in embryonic brain development is discussed.
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Den et al. (1970) studied this question.
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