A discussion of the evidence for a mechanism of action of vitamin A at the transcriptional, translational, and posttranslational levels is presented. The conclusion that retinol may be acting at the posttranslational level is based on the following findings. The in vivo and in vitro biosynthesis of a specific glycopeptide is greatly decreased in vitamin A deficiency. This glycopeptide contains D-fucose, D-galactose, D-glucosamine, D-galactosamine, and D-sialic acid in the molar ratios 1.00:1.73:0.87: 1.97:0.49, respectively. By indirect immunofluorescence the glycopeptide was localized in the goblet cell. The number of these cells, as revealed by periodic acid-Schiff staining, was greatly decreased in vitamin A deficiency. When (H3) retinol and guanosine-diphosphate-mannose (C14) are incubated in the presence of a membrane-rich fraction from rat or hamster liver or intestinal mucosa, a double-labeled mannolipid is isolated. This mannolipid can donate mannose to endogenous acceptors. These findings strongly suggest that retinol may be functioning in the biosynthesis of glycoproteins by carrying monosaccharides.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)