Studies on the activation by dolichol-P-mannose of the biosynthesis of GlcNAc-P-P-dolichol and the topography of the GlcNAc-transferases concerned with the synthesis of GlcNAc-P-P-dolichol and (GlcNAc)2-P-P-dolichol: a review.
A review is presented of research carried out in this laboratory on two aspects of the dolichol pathway that may have regulatory influences on these events. (i) The validity of the phenomenon of the activation of the biosynthesis of GlcNAc-P-P-dolichol and (GlcNAc)2-P-P-dolichol by dolichol-P-mannose is supported by experiments carried out on the Thy-1-negative mouse lymphoma cell. While this cell cannot synthesize the activating compound, this capacity was retained and revealed upon the addition of exogenous dolichol-P-mannose. (ii) The topographical orientation of the GlcNAc-transferases that catalyze the biosynthesis of GlcNAc-P-P-dolichol and (GlcNAc)2-P-P-dolichol was investigated in microsomes from the liver of the embryonic chick using dolichol phosphate liposomes as an exogenous substrate. The formation of GlcNAc-P-P-dolichol and (GlcNAc)2-P-P-dolichol was inhibited by trypsinization under conditions where the native orientation of the microsome was maintained, as indicated by the latency of mannose-6-phosphatase. Both GlcNAc-lipids were detected on free liposomes after incubation with intact microsomes, and in the same proportions as found on the microsome. From these and other studies, evidence was obtained indicating the cytoplasmic orientation of the GlcNAc-transferases that catalyze the synthesis of the first two intermediates of the dolichol pathway.