Electron paramagnetic resonance spectroscopic and electrochemical characterization of the partially purified N5-methyltetrahydromethanopterin:coenzyme M methyltransferase from Methanosarcina mazei Gö1.
The N5-methyltetrahydromethanopterin:coenzyme M methyltransferase is a membrane-bound cobalamin-containing protein of Methanosarcina mazei Gö1 that couples the methylation of coenzyme M by methyltetra-hydrosarcinopterin to the translocation of Na+ across the cell membrane (B. Becher, V. Müller, and G. Gottschalk, J. Bacteriol. 174:7656-7660, 1992). We have partially purified this enzyme and shown that, in addition to the cobamide, at least one iron-sulfur cluster is essential for the transmethylation reaction. The membrane fraction or the partly purified protein contains a "base-on" cobamide with a standard reduction potential (Eo') for the Co2+/1+ couple of -426 mV. The iron-sulfur cluster appears to be a [4Fe-4S]2+/1+ type with an Eo' value of -215 mV. We have determined the methyltransferase activity at various controlled redox potentials and demonstrated that the enzyme activity is activated by a one-electron reduction with half-maximum activity occurring at -235 mV in the presence of ATP and -450 mV in its absence. No activation was observed when ATP was replaced by other nucleoside triphosphates or nonhydrolyzable ATP analogs.
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Department of Biochemistry, University of Nebraska, Lincoln 68583-0718, USA.
Becher
B
B
Gottschalk
G
G
Ragsdale
S W
SW
D000255:Adenosine Triphosphate / Q000494:pharmacology; D003038:Cobamides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D015080:Mesna / Q000378:metabolism*; D017020:Methanosarcina / Q000201:enzymology*; D008780:Methyltransferases / Q000737:chemistry / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D011199:Potentiometry; D011622:Pterins / Q000378:metabolism*
D003038:Cobamides; D007506:Iron-Sulfur Proteins; D011622:Pterins; D000255:Adenosine Triphosphate; C073313:5-methyl-5,6,7,8-tetrahydro-methanopterin; D008780:Methyltransferases; C048755:tetrahydromethanopterin S-methyltransferase; D015080:Mesna