Roles for the Two 1-Butanol Dehydrogenases ofPseudomonas butanovorain Butane and 1-Butanol Metabolism

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Abstract
Pseudomonas butanovoragrown on butane or 1-butanol expresses two 1-butanol dehydrogenases, a quinoprotein (BOH) and a quinohemoprotein (BDH). BOH exhibited high affinity towards 1-butanol (Km= 1.7 ± 0.2 μM). BOH also oxidized butyraldehyde and 2-butanol (Km= 369 ± 85 μM andKm= 662 ± 98 μM, respectively). The mRNA induction profiles of BOH and BDH at three different levels of 1-butanol, a nontoxic level (0.1 mM), a growth-supporting level (2 mM), and a toxic level (40 mM), were similar. When cells were grown in citrate-containing medium in the presence of different levels of 1-butanol, wild-typeP. butanovoracould tolerate higher levels of 1-butanol than theP. butanovora boh::tetstrain and theP. butanovora bdh::kanstrain. A model is proposed in which the electrons from 1-butanol oxidation follow a branched electron transport chain. BOH may be coupled to ubiquinone, with the electrons being transported to a cyanide-sensitive terminal oxidase. In contrast, electrons from BDH may be transferred to a terminal oxidase that is less sensitive to cyanide. The former pathway may function primarily in energy generation, while the latter may be more important in the detoxification of 1-butanol.