Glycoprotein Biosynthesis in Peripheral Nervous System Myelin: Effect of Tunicamycin

Abstract: The effect of an inhibitor of N -glycosylation of glycoproteins, tunicamycin, on synthesis of PNS myelin proteins was investigated in vitro by using chopped sciatic nerves or spinal roots of 21-day-old Wistar rats. Tunicamycin when incubated with these nerves in the presence of ³H-labeled fucose, mannose, or glucosamine inhibited the uptake of radioactivity into myelin proteins including some high-molecular-weight proteins, P₀, 23K protein, and 19K protein by amounts ranging from 42 to 79%. Uptake of ¹⁴Camino acid mixture was inhibited much less by tunicamycin, but a new radioactive protein peak appeared when the protein mixtures had been separated by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. This protein ran directly in front of the P₀ peak, did not correspond to any bands stained by Fast green, and was not labeled by fucose. This peak appeared in increasing larger proportions with progressive time of incubation of nerves with ³H amino acids in the presence of tunicamycin. The new protein, which cross-reacts with P₀ antiserum, was tentatively identified as a nonglycosylated P₀ protein that appears to be almost as well incorporated as P₀ into the subcellular fraction containing myelin. At this time it is not possible to determine whether the unglycosylated P₀ is actually assembled into a site and configuration like that of P₀.