Effects of exogenous retinol and retinoic acid on the biosynthesis of carbon 14 mannose labeled glyco lipids and glyco proteins in rat liver

Sato, M.; Deluca, L.M.; Muto, Y.

Journal of Nutritional Science and Vitaminology 24(1): 9-24


ISSN/ISBN: 0301-4800
Accession: 005303233

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The in vivo and in vitro effects of retinol and retinoic acid on the synthesis of mannolipids and mannopeptides in rat liver were investigated. The incorporation of 14C-mannose into glycolipids and glycoproteins showed a decrease in vitamin A-depleted rats compared with vitamin A-fed rats. By DEAE-cellulose, silicic acid and TLC, the mannose-containing lipids were separated into mannosyl retinyl phosphate (MRP, Rf 0.2) and dolichyl mannosyl phosphate (DMP, Rf 0.4), respectively. A rapid increase in the synthesis of labeled MRP was observed, exhibiting a peak between 25-60 min after i.p. administration of retinol to vitamin A-depleted rats. Similarly, administration of retinoic acid brought about elevation of 14C-mannolipid (Rf 0.2) synthesis with a peak at 60 min after injection. The incorporation of 14C-mannose into DMP (Rf 0.4) remained unchanged by such treatment. In vitro addition of retinyl phosphate, but not retinoyl phosphate, markedly stimulated the synthesis of 14C-mannolipid (Rf 0.2), using crude membrane of rat liver and GDP-14C-mannose as the donor. Apparently, not only retinol but also retinoic acid plays an important biological role in mannosyl transfer reaction in rat liver. The molecular participation of a metabolite of retinoic acid in the formation of a mannolipid and the structure of such a metabolite remain to be established.