title: Activation of dolichyl-phospho-mannose synthase by phospholipids.
abstract: Dolichyl-phospho-mannose synthase, or GDPmannose:dolichyl-phosphate mannosyltransferase (EC 2.4.1.83), was solubilized from rat liver microsomes with 1.0% Nonidet P-40 and the enzyme was further purified by column chromatography on DEAE-cellulose in the presence of 0.1% Nonidet P-40. The purified enzyme preparation (880-fold over microsomes) was unstable in the presence of detergent and had no activity in the presence of Nonidet P-40, Triton X-100, octyl beta-glucoside, or deoxycholate. Detergent-free enzyme was active in the presence of phosphatidylethanolamine (PtdEtn) and in the presence of phospholipid mixtures of PtdEtn and phosphatidylcholine (PtdCho) when the molar proportion of PtdCho was 70% or less. The enzyme was inactive in the presence of PtdCho alone. Unsaturated species of PtdEtn have a tendency to destabilize membrane bilayers [Cullis, P. R. & de Kruijff, B. (1978) Biochim. Biophys. Acta 507, 207-218] and we have shown that dolichol promotes the destabilizing effect of PtdEtn on membranes composed of PtdCho and PtdEtn [Jensen, J. W. & Schutzbach, J. S. (1984) Biochemistry 23, 115-1119]. These results suggest that dolichyl-P-mannose synthase is optimally active in a phospholipid matrix that contains some component phospholipids that prefer non-bilayer structural organization in isolation. Heat-inactivation and sedimentation experiments demonstrated that the synthase associated with PtdEtn in the presence of dolichyl-P. The PtdEtn-reconstituted enzyme catalyzed the reversible transfer of mannose from GDP-mannose to dolichyl-P. The Km for GDP-mannose was found to be 0.69 microM and the apparent Km for dolichyl-P was 0.3 microM. GMP, GDP, and GTP inhibited mannosyl transfer 50% at concentrations of 16 microM, 1.3 microM and 3 microM respectively.
mesh_terms: D000818:Animals; D002021:Buffers; D002848:Chromatography, DEAE-Cellulose; D004287:Dolichol Monophosphate Mannose / Q000032:analysis; D004789:Enzyme Activation / Q000187:drug effects; D006602:Hexosyltransferases / Q000378:metabolism*; D008364:Mannosyltransferases / Q000032:analysis / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D010743:Phospholipids / Q000494:pharmacology*; D051381:Rats; D012995:Solubility
chemical_list: D002021:Buffers; D010743:Phospholipids; D004287:Dolichol Monophosphate Mannose; D006602:Hexosyltransferases; D008364:Mannosyltransferases; C022755:dolichyl-phosphate beta-D-mannosyltransferase