Xylosylphosphoryldolichol synthesized by chick embryo epiphyses. Not an intermediate in proteoglycan biosynthesis.

Incubation of chick embryo epiphyseal microsomes with UDP-[14C]xylose in the presence of pyrophosphatase inhibitors resulted in the incorporation of [14C]xylose into proteoglycan and the formation of small amounts of 14C-labeled material soluble in chloroform:methanol. Synthesis of the [14C]xylose-lipid was stimulated by exogenous dolichol phosphate whereas the addition of retinol plus ATP had no effect. The [14C]xylosyl-lipid was identified as [14C]xylosylphosphoryldolichol by chromatography on SG-81 paper and DEAE-cellulose and by acid hydrolysis. Addition of UDP-galactose and UDP-glucuronic acid to incubations of epiphyseal microsomes with UDP-[14C]xylose did not stimulate [14C]xylose incorporation into lipid nor into proteoglycan. Under several different conditions, [14C]xylose was not transferred from [14C]xylosylphosphoryldolichol to proteoglycan, indicating that [14C]xylosylphosphoryldolichol was not an intermediate in proteoglycan biosynthesis. Chick embryo epiphyseal microsomes also synthesized [14C]glucosylphosphoryldolichol. In addition, [14C]glucose was transferred from [14C]glucosylphosphoryldolichol into oligosaccharide lipids in the chloroform:methanol:water extract and into glycoproteins in the pellet fraction. Competition experiments with UDP-glucose and UDP-xylose suggested that xylosylphosphoryldolichol was synthesized by the glucosyltransferase involved with glucosylphosphoryldolichol biosynthesis.