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J. Bacteriol., Feb 1997, 846-852, Vol 179, No. 3
DJ Ferguson Jr and JA Krzycki
Reconstitution of trimethylamine-dependent coenzyme M (CoM) methylation was
achieved with three purified polypeptides. Two of these polypeptides
copurified as a trimethylamine methyl transfer (TMA-MT) activity detected
by stimulation of the TMA:CoM methyl transfer reaction in cell extracts.
The purified TMA-MT fraction stimulated the rate of methyl-CoM formation
sevenfold, up to 1.7 micromol/min/mg of TMA-MT protein. The TMA-MT
polypeptides had molecular masses of 52 and 26 kDa. Gel permeation of the
TMA-MT fraction demonstrated that the 52- kDa polypeptide eluted with an
apparent molecular mass of 280 kDa. The 26-kDa protein eluted primarily as
a monomer, but some 26-kDa polypeptides also eluted with the 280-kDa peak,
indicating that the two proteins weakly associate. The two polypeptides
could be completely separated using gel permeation in the presence of
sodium dodecyl sulfate. The corrinoid remained associated with the 26-kDa
polypeptide at a molar ratio of 1.1 corrin/26-kDa polypeptide. This
polypeptide was therefore designated the TMA corrinoid protein, or TCP. The
TMA-MT polypeptides, when supplemented with purified methylcorrinoid:CoM
methyltransferase (MT2), could effect the demethylation of TMA with the
subsequent methylation of CoM and the production of dimethylamine at
specific activities of up to 600 nmol/min/mg of TMA-MT protein. Neither
dimethylamine nor monomethylamine served as the substrate, and the activity
required Ti(III) citrate and methyl viologen. TMA-MT could interact with
either isozyme of MT2 but had the greatest affinity for the A isozyme.
These results suggest that TCP is uniquely involved in TMA-dependent
methanogenesis, that this corrinoid protein is methylated by the substrate
and demethylated by either isozyme of MT2, and that the predominant isozyme
of MT2 found in TMA-grown cells is the favored participant in the TMA:CoM
methyl transfer reaction.
Copyright © 1997, American Society for Microbiology
Reconstitution of trimethylamine-dependent coenzyme M methylation with the trimethylamine corrinoid protein and the isozymes of methyltransferase II from Methanosarcina barkeri
Department of Microbiology, Ohio State University, Columbus 43210, USA.
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