The goals are to continue the characterization of the differentiation of chick embryo tibial chondrocytes with special emphasis on the changing metabolism of chondroitin SO4 as the chondrocytes differentiate and the role of chondroitin SO4 in the calcification events. Work will continue on the characterization of the differentiated state of the chondrocytes from different zones of the tibia, focussing on the changes in the structures of the N-linked oligosaccharides on the several species of proteochondroitin SO4 and the structural differences in the nuclear heparan SO4 in chondrocytes from different tibial zones. The biosynthesis of chondroitin SO4 using cell extracts from chondrocytes will be studied, with particular emphasis on (a) the development of additional membrane-permeable glycosyl and sulfuryl acceptors so that the effect of the intraluminal environment of the Golgi vesicles on the extents of chain elongation and sulfation can be examined, (b) the conditions that regulate the ratios of 6- to 4-sulfation, and (c) the interorganelle transport of biosynthetic intermediates through the Golgi. Also, the formation of matrix vesicles by cultured chondrocytes will be studied to determine what factors control the delivery of alkaline phosphatase, Type X collagen, Ca2+, and Pi to the vesicles.
