Influence of metal ions on the biosynthesis of N-acetylglucosaminyl polyprenols by the retina.
The following enzymatic process was investigated, catalyzed by an enzyme preparation from the retina of the embryonic chick: UDP-GlcNAc + dolichol phosphate GDPmannose leads to metal ions GlcNAc-P-P-polyprenol + (GlcNAc)2-P-P-polyprenol + Man-(GlcNAc)2-P-P-polyprenol. These reactions were carried out in the presence of a dolichol phosphate mannose-synthesizing system, shown previously to be an activator of GlcNAc-lipid synthesis. The process was also strongly influenced by the choice of the divalent cation used during the reactions. In the presence of Mg2+, not only was the extent of incorporation of radioactivity from UDP-[3H]GlcNAc increased 4-fold into the GlcNAc lipids, as compared to Mn2+, but the relative distribution of the products was affected as well. In the presence of Mg2+ the reaction was driven mainly in the direction of the formation of the first intermediate of the dolichol pathway, GlcNAc-P-P-polyprenol. Many of the other characteristics of the GlcNAc-transferases, such as pH optimum, requirement for dolichol phosphate and specificity for stimulation by sugar nucleotides, were similar for either the Mn2+ or Mg2+ systems. Retinol phosphate could not replace the requirement for dolichol phosphate. The influence of metal ions, in addition to the stimulation by dolichol phosphate mannose, on GlcNAc-lipid synthesis may be aspects of metabolic regulation of the dolichol pathway.
D000818:Animals; D002413:Cations, Divalent; D002642:Chick Embryo; D006155:Guanosine Diphosphate Mannose / Q000378:metabolism; D007700:Kinetics; D011103:Polyisoprenyl Phosphate Monosaccharides / Q000096:biosynthesis*; D011105:Polyisoprenyl Phosphate Sugars / Q000096:biosynthesis*; D012160:Retina / Q000201:enzymology*; D013379:Substrate Specificity; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism
D002413:Cations, Divalent; D011103:Polyisoprenyl Phosphate Monosaccharides; D011105:Polyisoprenyl Phosphate Sugars; D006155:Guanosine Diphosphate Mannose; D014537:Uridine Diphosphate N-Acetylglucosamine; C018439:N-acetylglucosaminylpyrophosphoryldolichol