title: The dolichol pathway of protein glycosylation in rat liver. Evidence that GTP promotes transformation of endogenous dolichyl phosphate into dolichylpyrophosphoryl-N-acetylglucosamine in stripped rough microsomes.
abstract: Tunicamycin, an antibiotic which inhibits the transfer of N-acetylglucosamine 1-phosphate to dolichyl phosphate, has been used to decide whether or not, in stripped rough microsomes incubated with UDP-N-acetylglucosamine and GDP-mannose in the absence of detergent, the earliest effect of GTP in core glycosylation of proteins is to enhance synthesis of dolichylpyrophosphoryl-N-acetylglucosamine from endogenous dolichyl phosphate, or to transform this monoglycoside derivative into dolichylpyrophosphorylchitobiose. It has been found that the presence of tunicamycin in the reaction medium annihilates incorporation of N-acetylglucosamine and mannose into all kinds of glycoside derivative of dolichyl pyrophosphate, whereas dolichylphosphorylmannose is then formed in greater amount. Incorporation of N-acetylglucosamine into protein was also abolished; that of mannose was considerably reduced. Other experiments showed that transfer of N-acetylglucosamine 1-phosphate is the only reaction of the lipid intermediates pathway that becomes limiting after addition of tunicamycin in our GTP-stimulated system. Taking these and previous results from this laboratory [Godelaine et al. (1979) Eur. J. Biochem. 96, 17-26 and 27-34] into account, we conclude that GTP enhances the transformation of endogenous dolichyl phosphate into dolichylpyrophosphoryl-N-acetylglucosamine and leads to the complete assembly of dolichol-linked oligosaccharides which become ultimately transferred to protein. Triton X-100 increased the amount of dolichol glycosylated and markedly raised the ratio of labelled dolichylpyrophosphorylchitobiose to dolichylpyrophosphoryl-N-acetylglucosamine. Such changes being induced by GTP, we suggest that this nucleotide makes it possible to overcome a structural barrier of rough microsomes.
mesh_terms: D000818:Animals; D001711:Biotransformation; D055598:Chemical Phenomena; D002621:Chemistry; D004288:Dolichol Phosphates / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D011103:Polyisoprenyl Phosphate Monosaccharides / Q000096:biosynthesis*; D011105:Polyisoprenyl Phosphate Sugars / Q000096:biosynthesis*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D004288:Dolichol Phosphates; D011103:Polyisoprenyl Phosphate Monosaccharides; D011105:Polyisoprenyl Phosphate Sugars; D011106:Polyisoprenyl Phosphates; D011506:Proteins; D014415:Tunicamycin; C028306:dolichol monophosphate; C018439:N-acetylglucosaminylpyrophosphoryldolichol; D006160:Guanosine Triphosphate