Synthesis of Glycoproteins and Ganglio‐sides in Developing Rat Brain

Intracerebral injections of radioactive fucose into developing rats resulted in specific labelling of the brain glycoproteins in their fucose moieties. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate revealed that the radioactive glycoproteins were very heterogeneous with regard to molecular weight. A procedure utilizing [3H]fucose and [14C]fucose together with double‐label counting techniques was developed for comparing the electrophoretic patterns of newly synthesized glycoproteins from different samples of tissue. By the use of this procedure we showed that the incorporation of radioactive fucose into the glycoproteins of high mol. wt. was relatively greater in the brains of 5‐day‐old rats than in those of 25‐day‐old rats. Intracerebral injection of N‐[Ac‐3H]acetyl‐d‐mannosamine resulted in a high degree of specificity for the labelling of sialic acid moieties in glycoproteins and gangliosides. The ratio of the d.p.m. of N‐[3H]acetylmannosamine incorporated into glycoproteins to the d.p.m. incorporated into gangliosides was higher in 5‐day‐old rats than in 15‐ or 25‐day‐old rats. Experiments in which 15‐day‐old rats were injected with a mixture of [14C]fucose and N‐[3H]acetylmannosamine showed that there were differences in the relative degrees of incorporation of the two radioactive precursors into the various glycoproteins. The greatest incorporation of [14C]fucose relative to that of N‐[3H]acetylmannosamine occurred in some of the glycoproteins of smaller mol. wt.