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A low-molecular-mass protein from Methylococcus capsulatus (Bath) is responsible for the regulation of formaldehyde dehydrogenase activity in vitro

Stephen Tate

Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK

Author for correspondence: Howard Dalton. Tel: +44 1203 523552. Fax: +44 1203 523568. e-mail: hd@dna.bio.warwick.ac.uk

ABSTRACT

Summary: An 8·6 kDa protein, which the authors call a modifin, has been purified from Methylococcus capsulatus (Bath) and has been shown to alter the substrate specificity and kinetics of NAD⁺-linked formaldehyde dehydrogenase (FDH) isolated from the same organism. Purification methods for both the modifin and FDH are presented which reliably produced pure protein for further analysis. Analysis of the molecular mass and N-terminal sequence of both FDH and the modifin indicate that they are unique proteins and show no similarity to alcohol or aldehyde dehydrogenase enzymes isolated from methylotrophic bacteria. Substrate specificity studies demonstrated that FDH oxidized formaldehyde exclusively in the presence of the modifin; a diverse range of aldehydes and alcohols were oxidized by FDH in the absence of the modifin. No formaldehyde oxidation was detected in the absence of the modifin. Attempts to replace the modifin with glutathione or high concentrations of methanol to stimulate formaldehyde oxidation failed. With acetaldehyde as substrate, FDH showed standard Michaelis-Menten kinetics; interaction of FDH reaction to sigmoidal. Kinetic analysis during turnover experiments indicated that the FDH may be associated with bound formaldehyde following enzyme isolation and that NAD may also be associated with the enzyme but in a form that is less tightly bound than found with the methanol dehydrogenase from Bacillus methanolicus. Data are presented which indicate that the modifin may play an important role in regulating formaldehyde concentration in vivo.

Present address: Delta Biotechnology Ltd, Castle Court, Castle Boulevard, Nottingham NG7 1FD, UK.

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