A single enzyme catalyzes the synthesis of the mannosylphosphoryl derivative of dolichol and retinol in rat liver and Chinese hamster ovary cells.

Abstract It is well established that mannosylphosphoryldolichol participates in the synthesis of N-linked glycoproteins by donating mannosyl residues to oligosaccharide-lipid intermediates. It has been suggested that mannosylphosphorylretinol also is involved in glycoprotein biosynthesis. We conclude that one synthase catalyzes the synthesis of both mannosylphosphoryldolichol and mannosylphosphorylretinol in rat liver tissue and Chinese hamster ovary cells, based on the following results. 1) The enzyme in rat liver microsomes that synthesizes mannosylphosphoryldolichol and mannosylphosphorylretinol is inactivated at the same rate at 55 degrees C. 2) In membranes of both rat liver and Chinese hamster ovary cells, exogenous dolichyl phosphate and retinyl phosphate compete with each other for mannosyl-lipid synthesis. However, in both systems adding exogenous retinyl phosphate has no effect on the synthesis of mannosylphosphoryldolichol from endogenous dolichyl phosphate in the membranes. 3) Membranes prepared from a mutant of Chinese hamster ovary cells which is devoid of mannosylphosphoryldolichol synthase lack the ability to synthesize mannosylphosphorylretinol.