Long-chain alcohol and aldehyde dehydrogenase activities in Acinetobacter calcoaceticus strain HO1-N

Three alcohol dehydrogenases have been identified in Acinetobacter calcoaceticus sp. strain HO1-N: an NAD+-dependent enzyme and two NADP+-dependent enzymes. One of the NADP+-dependent alcohol dehydrogenases was partially purified and was specific for long-chain substrates. With tetradecanol as substrate an apparent K m value of 5.2 μM was calculated. This enzyme has a pI of 4.5 and a molecular mass of 144 kDa. All three alcohol dehydrogenases were constitutively expressed. Three aldehyde dehydrogenases were also identified: an NAD+-dependent enzyme, an NADP+-dependent enzyme and one which was nucleotide independent. The NAD+-dependent enzyme represented only 2% of the total activity and was not studied further. The NADP+-dependent enzyme was strongly induced by growth of cells on alkanes and was associated with hydrocarbon vesicles. With tetradecanal as substrate an apparent K m value of 0.2 μM was calculated. The nucleotide-independent aldehyde dehydrogenase could use either Wurster's Blue or phenazine methosulphate (PMS) as an artificial electron acceptor. This enzyme represents approximately 80% of the total long-chain aldehyde oxidizing activity within the cell when the enzymes were induced by growing the cells on hexadecane. It is particulate but can be solubilized using Triton X-100. The enzyme has an apparent K m of 0.36 mM for decanal.