Methane—make it or break it

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Science  20 May 2016:
Vol. 352, Issue 6288, pp. 892-893
DOI: 10.1126/science.aaf7700

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About 500 to 600 million metric tons of methane, a potent greenhouse gas, are emitted annually worldwide; ~69% of this methane is produced biologically by anaerobic archaea known as methanogens (1). In some environments, methane emissions are partly offset by anaerobic methane oxidizing archaea (ANME) and aerobic methanotrophic bacteria (1). In methanogens, the methyl-coenzyme M reductase (MCR) enzyme uses a nickel-containing cofactor (F430) to catalyze the final step of methane synthesis (see the figure, panels A and B) (2, 3). The MCR reaction is reversible, and MCR may also catalyze the first step of methane oxidation by ANME (2). The MCR catalytic cycle begins with F430 in the reduced Ni(I) form (4), but what happens next has been unclear. On page 953 of this issue, Wongnate et al. (5) report evidence for a Ni(II)-thiolate intermediate.