Biosynthesis of chondroitin sulfate proteoglycan. Subcellular distribution of glycosyltransferases in embryonic chick brain.

The subcellular distributions of five glycoslytransferases involved in the biosynthesis of the chondroitin sulfate proteoglycan and of a sixth glycosyltransferase, presumably involved in glycoprotein biosynthesis, were examined in 13-day chick enbryo brain. Fractionation studies performed by the procedure of Gray and Whittaker (Gray, E.G., and Whittaker, V.P. (1962) J. Anat. (London) 96, 79-88) revealed that three of the six enzymes were directly associated with the membrane fraction of synaptosome-enriched preparations; varying amounts of the remaining glycosyltransferases were distributed between the 100,000 times g supernatant and the synaptosome-enriched fraction after differential and density gradient centrifugation of crude chick brain homogenates. The time of appearance of three of the glycosyltransferases was examined in chick embryo brain tissue at several stages of development. The brain content of each glycosyltransferase increased rapidly between day 7 and hatching at day 21. A sharp decline in each of the glycosyltransferase activities occurred at hatching.