The reactivity of [ 1,4,7,10,13-pentaazacyclohexadecane-14,16-dionato(2-)] nickel(II), NinL, toward H3CSCH2CH2SO3-, methyl-coenzyme M, possesses striking similarities to the active site chemistry of methyl-coenzyme M reductase, which contains the nickel tetrapyrrole species F430. The initial rate of substrate conversion for a series of substrate analogues of the formula RX(CH2)"Y" is reported, where the R and X groups have the greatest influence on reactivity. When R = CH3 and X = S, little change in reactivity is observed when = 2, 3, or 6 or when Y" = S03", C02", or P03". These results are consistent with the two-site model for substrate binding at F430, the proposed enzyme active site.
The nickel tetrapyrrole containing factor, F430, is implicated in the final methane evolution step in methanogenic bacteria1"4 and has attracted considerable attention.5"8 The essential role of F430 in methane formation was demonstrated by Ankel-Fuchs and Thauer, who reported the in vitro catalysis of H3CSCH2C-H2S03", methyl coenzyme M (methyl-CoM), to methane and CoM by purified methyl-CoM reductase under reducing conditions.9 Since F430 exists in both the Ni(I) (or Ni(III)) and the Ni(II) states in Methanobacterium thermoautotrophicum,10,11 it is of interest to examine the role of the nickel ion oxidation state12•13 in methyl-CoM catalysis. We have found both the mono-and the divalent oxidation states of the water-soluble Ni(dioxo[16]-aneN5), NiL, complex14 catalyze methyl-CoM to methane and CoM.In a typical reaction NinL (0.267 mM) in deoxygenated distilled
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