Specific lipids enhance the activity of UDP-GlcNAc: dolichol phosphate GlcNAc-1-phosphate transferase in rat liver endoplasmic reticulum membrane vesicles.
The rate of the reaction catalyzed by UDP-N-acetylglucosamine (GlcNAc):dolichol phosphate GlcNAc-1-phosphate transferase in rat liver endoplasmic reticulum vesicles was shown to be influenced by particular lipids. Utilizing in vitro assay conditions where the membrane vesicles retained latency of glucose-6-phosphatase activity, the addition of phosphatidylethanolamine, cardiolipin, or monogalactosyldiglyceride resulted in severalfold increases in the rate of dolichol pyrophosphate N-acetylglucosamine synthesis. Other phospholipids were not stimulatory. These rates were dependent on the concentrations of the exogenous lipids and of the substrate dolichol phosphate. In the presence of cardiolipin, the membrane-bound enzyme became more susceptible to inactivation by protease K and to inhibition by tunicamycin. Titration of cardiolipin-containing endoplasmic reticulum vesicles with adriamycin indicated that the majority of the cardiolipin was exposed on the outer surface. These results suggest that the particular lipids altered membrane structure in a way that allowed further access of the enzyme to substrate, inhibitor, and other molecules. Lipids observed in these studies to be stimulatory are known to exist in the macromolecular hexagonal phase and may therefore be affecting the GlcNAc-1-phosphate transferase by locally disrupting the bilayer structure of the membrane. As other dolichol-utilizing enzymes have been previously observed by other investigators to be similarly influenced by such lipids, the effects may be common to enzymes of the dolichol cycle.
Chandra
N C
NC
Department of Chemistry and Biochemistry, University of Notre Dame, Indiana 46556.
Doody
M B
MB
Bretthauer
R K
RK
D000818:Animals; D002308:Cardiolipins / Q000737:chemistry; D004317:Doxorubicin / Q000737:chemistry / Q000494:pharmacology; D019286:Endopeptidase K; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D006868:Hydrolysis; D007425:Intracellular Membranes / Q000737:chemistry / Q000201:enzymology*; D008297:Male; D008360:Mannosephosphates / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry*; D008862:Microsomes, Liver / Q000201:enzymology*; D017830:Octoxynol; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry; D010770:Phosphotransferases / Q000378:metabolism*; D011092:Polyethylene Glycols; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012697:Serine Endopeptidases / Q000494:pharmacology; D013379:Substrate Specificity / Q000187:drug effects; D017855:Transferases (Other Substituted Phosphate Groups); D014415:Tunicamycin / Q000494:pharmacology
D002308:Cardiolipins; D008360:Mannosephosphates; D008563:Membrane Lipids; D014415:Tunicamycin; C027693:mannose-6-phosphate; D011092:Polyethylene Glycols; D004317:Doxorubicin; D017830:Octoxynol; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C023222:UDPacetylglucosamine-dolichyl-phosphate acetylglucosamine-1-phosphate transferase; C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; D005952:Glucose-6-Phosphatase; D012697:Serine Endopeptidases; D019286:Endopeptidase K