Soluble Alcohol Dehydrogenases

Alcohol ^ Aldehyde

A bacterial strain that is able to utilize several kinds of alcohols as its sole carbon and energy sources was isolated from soil and tentatively identified as Pseudomonas putida HK5 [20]. Three distinct dye-linked ADHs, each of which contains PQQ as the prosthetic group, are formed in the periplasmic space of the strain grown on different alcohols and thus the enzyme activities appear in the cell-free extract in soluble form.

ADH I is formed most abundantly in the cells grown on ethanol and is similar to the quinoprotein ADH reported from P. putida [21], except for its isoelectric point. The other two ADHs, ADH IIB and ADH IIG, are formed separately in the cells grown on 1-butanol and 1,2-propandiol, respectively. Both of these enzymes contain heme c in addition to PQQ and function as quinohemoprotein dehydrogenases. Thus, potassium ferricyanide is an available electron acceptor for ADHs IIB and IIG but not for ADH I. The molecular masses are estimated to be 69 kDa for ADH IIB and 72 kDa for ADH IIG, and both enzymes have been shown to be monomers.

Antibodies raised against each of the purified ADHs could distinguish the ADHs from one another. Immunoblot analysis showed that ADH I is detected in cells grown on each alcohol tested, but ethanol was the most effective inducer. ADH IIB is formed in cells grown on alcohols of medium chain length and also on 1,3-butanediol. Induction of ADH IIG is restricted to 1,2-propanediol or glycerol, of which the former alcohol is more effective. These results from immunoblot analysis correlate well with the substrate specificities of the respective enzymes. Thus, three distinct quinoprotein ADHs are formed by a single bacterium under different growth conditions. Molecular cloning and structural analysis of ADH IIB and ADH IIG have been reported [16, 17, 22]. These soluble forms of ADHs are also used for alcohol sensors. Of the three different PQQ-dependent ADHs, ADH IIG would be the most convincing for use as a glycerol sensor for a neutral fat diagnostic test by combining with lipoprotein lipase.

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