RADIOACTIVE FUCOSE AS A TOOL FOR STUDYING GLYCOPROTEIN-SECRETION

The efficiency and reliability of radioactive fucose as a specific lab el for newly synthesized glycoproteins were investigated. Young adult male rabbits were injected intravitreally with [H-3]-fucose, [H-3]-gal actose, [H-3]-mannose, N-acetyl-[H-3]-glucosamine or N-acetyl-[H-3]-ma nnosamine, and killed 40 h after injection. In another series of exper iments rabbits were injected with either [H-3]-fucose or several triti ated amino acids and the specific activity of the vitreous proteins wa s determined. Vitreous samples were also processed by sodium dodecyl s ulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and histological sections of retina, ciliary body and lens (the eye components around t he vitreous body) were processed for radioautography. The specific act ivity (counts per minute per microgram of protein) of the glycoprotein s labeled with [H-3]-fucose was always much higher than that of the pr oteins labeled with any of the other monosaccharides or any of the ami no acids. There was a good correlation between the specific activity o f the proteins labeled by any of the above precursors and the density of the vitreous protein bands detected by fluorography. This was also true for the silver grain density on the radioautographs of the histol ogical sections of retina, ciliary body and lens. The contribution of radioautography (after [H-3]-fucose administration) to the elucidation of the biogenesis of lysosomal and membrane glycoproteins and to the determination of the intracellular process of protein secretion was re viewed. Radioactive fucose is the precursor of choice for studying gly coprotein secretion because it is specific, efficient and practical fo r this purpose.