Lothar Jaenicke and C₁-metabolism: his first 25 years of research

Abstract

Abstract:The biochemist Lothar Jaenicke died on 29 December 2015, aged 92 years old. The last time I saw him was at his 90 th birthday on 14 September 2013, at the occasion of which his colleagues at the Universität zu Köln (Cologne) in Germany had organized a symposium to honor him.

Methyl (Alkyl)-Coenzyme M Reductases: Nickel F-430-Containing Enzymes Involved in Anaerobic Methane Formation and in Anaerobic Oxidation of Methane or of Short Chain Alkanes

“…157,158 The S N 2 proposal was also based on the property of cobalamin-dependent methionine synthase to catalyze the formation of methyl-cob(III)alamin from methionine, which is also a methylthioether (Δ G 0 ′ = +30 kJ/mol). 159,160 An important mechanistic argument was that both reactions proceed with inversion of stereoconfiguration of the methyl group 144…”

“…The mechanism long favored by the author of this Perspective assumed methyl-Ni­(III)­F-430 and methyl-Ni­(II)­F-430 as intermediates in the MCR catalytic cycle, the methyl-Ni­(III) being formed by a nucleophilic attack by Ni­(I) of the methyl group of methyl-coenzyme M in an S N 2 reaction. , The proposal was based on the finding that 2 mol pentamethylester of Ni­(I)­F-430 (Ni­(I)­F-430M) reacts with 1 mol electrophilic methyl donors to 1 mol methane and 2 mol Ni­(II)­F-430 M and that paramagnetic methyl-Ni­(II)­F-430 M can be trapped as likely an intermediate . Ni­(I)­F-430 M is thus a nucleophile similar to cob­(I)­alamin with the difference that methyl-Ni­(III)­F-430 M is much easier to reduce to methyl-Ni­(II)­F-430 than methyl-cob­(III)­alamin to methyl-cob­(II)­alamin: the F-430-catalyzed reduction of methyl chloride with Ti­(III) is almost 50 times more rapid than the cobalamin-catalyzed reaction and does not generate ethane as a side product. , The S N 2 proposal was also based on the property of cobalamin-dependent methionine synthase to catalyze the formation of methyl-cob­(III)­alamin from methionine, which is also a methylthioether (Δ G 0 ′ = +30 kJ/mol). , An important mechanistic argument was that both reactions proceed with inversion of stereoconfiguration of the methyl group…”

“…157,158 The S N 2 proposal was also based on the property of cobalamin-dependent methionine synthase to catalyze the formation of methyl-cob(III)alamin from methionine, which is also a methylthioether (ΔG 0 ′ = +30 kJ/mol). 159,160 An important mechanistic argument was that both reactions proceed with inversion of stereoconfiguration of the methyl group 144 Experimental support for the S N 2 mechanism came from the laboratory of Steven Ragsdale and of Evert Duin reporting that Ni(I)F-430 in MCR can be alkylated with methyl bromide or methyl iodide to methyl-Ni(III)F-430, 91,161 the structure of which was elucidated by X-ray absorption spectroscopy (XAS) 162 and X-ray structure analysis. 120 The methyl-nickel complex in MCR was found to react with coenzyme M to methyl-coenzyme M and, e.g., with CoB 8 −SH, to Cob 8 −S-CH 3 , regenerating the MCR-red1 state 163 and with Ti(III) to methane and MCR-red1.…”