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Abstract
All organisms surveyed among a range of methylotrophic bacteria growing on both C1 and multi-carbon substrates contained a dye-linked formaldehyde dehydrogenase. The activity of this enzyme was very low in bacteria grown on C1 compounds when compared to the activities of other C1-specific enzymes and was not induced during growth on C1 compounds. The enzyme was partially purified (11-fold) from methanol- and ethanol-grown Hyphomicrobium X. Though not homogeneous, it did not contain methanol dehydrogenase, formate dehydrogenase or cytochrome c. Methylphenazonium methyl-sulphate (PMS), cytochrome c, Wurster’s Blue, dichlorophenol-indophenol (DCPIP) and methylphenazonium ethosulphate (PES) could act as the primary electron acceptors in the assay system with apparent K m values for the first three substances of 0·69, 128 and 3·07 μm, respectively. The activity of the partially purified enzyme could be maintained over 3 months at -20° in the presence of ethanol (10%, v/v). The molecular weight of the enzyme was 83500 ± 2500. It was active from pH 6·5 to 9·0 with maximum activity at pH 7·2 using cytochrome c as the electron acceptor and at pH 7·6 when PMS and DCPIP were used. Several different aldehydes could act as substrates; the apparent K m values for formaldehyde, acetaldehyde, propionaldehyde and heptaldehyde were 2860, 270, 13 and 2·5μm, respectively. Methanol and ethanol were not substrates. The dye-linked formaldehyde dehydrogenase is probably a general aldehyde dehydrogenase not directly involved in the dissimilation of C1 compounds.
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