Journal of Bacteriology, December 2001, p. 6832-6840, Vol. 183, No. 23
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.23.6832-6840.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


Department of Microbiology, Iowa State University, Ames, Iowa 50011
Received 17 May 2001/Accepted 11 September 2001
A membrane-associated, dye-linked formaldehyde dehydrogenase (DL-FalDH) was isolated from the obligate methylotroph Methylococcus capsulatus Bath. The enzyme was the major formaldehyde-oxidizing enzyme in cells cultured in high (above 1 µmol of Cu per mg of cell protein) copper medium and expressing the membrane-associated methane monooxygenase. Soluble NAD(P)+-linked formaldehyde oxidation was the major activity in cells cultured in low-copper medium and expressing the soluble methane monooxygenase (Tate and Dalton, Microbiology 145:159-167, 1999; Vorholt et al., J. Bacteriol. 180:5351-5356, 1998). The membrane-associated enzyme is a homotetramer with a subunit molecular mass of 49,500 Da. UV-visible absorption, electron paramagnetic resonance, and electrospray mass spectrometry suggest the redox cofactor of the DL-FalDH is pyrroloquinoline quinone (PQQ), with a PQQ-to-subunit stochiometry of approximately 1:1. The enzyme was specific for formaldehyde, oxidizing formaldehyde to formate, and utilized the cytochrome b559/569 complex as the physiological electron acceptor.
Present address: National Swine Research Center, USDA-ARS, Ames, IA
50011-3211.
Present address: Black Hills State University, Spearfish, SD
57799-9003.
§
Present address: Department of Chemistry and Biochemistry, Utah
State University, Logan, UT 84322-0300.
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