title: Inhibition of the methylcoenzyme M methylreductase system by NAD+ and NADP+ in cell-extracts of Methanosarcina barkeri.
abstract: In cell extracts of Methanosarcina barkeri, the methylcoenzyme M methylreductase system with H2 as the electron donor was inhibited by NAD+ and NADP+, but NADH and NADPH had no effect on enzyme activity. NAD+ (4 and 8 mM) shifted the saturation curve for methylcoenzyme M from hyperbolic (Hill coefficient [nH] = 1.0; concentration of substrate giving half maximal velocity [Km] = 0.21 mM) to sigmoidal (nH = 1.5 and 2.0), increased Km (Km = 0.25 and 0.34 mM), and slightly decreased Vmax. Similarly NADP+ at 4m and 8 mM increased nH to 1.6 and 1.85 respectively, but the Km values (0.3 and 0.56 mM) indicated that NADP+ was a more efficient inhibitor than NAD+.
mesh_terms: D004579:Electron Transport; D019605:Euryarchaeota / Q000201:enzymology*; D007700:Kinetics; D015080:Mesna / Q000037:antagonists & inhibitors; D009243:NAD / Q000494:pharmacology*; D009249:NADP / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*
chemical_list: D009243:NAD; D009249:NADP; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase; D015080:Mesna