The adh I and adh II genes encoding the alcohol dehydrogenase of an ethanologenic Zymomonas mobilis TISTR 405 have been cloned and characterized regarding their expression in Escherichia coli XL1 Blue. The adh I and adh II genes contain 1,014 and 1,152 nucleotides encoding 337 and 383 amino acid residues, respectively. The 405-ADH I and 405-ADH II proteins are highly conserved among Z. mobilis species but distant from the yeast genera Saccharomyces and Candida. The molecular weights of the expressed 405-ADH I or II proteins were 34 and 38 kDa, respectively. The ADH activity of the transformants expressing adh I and II was also detected via native PAGE at the same molecular weights. The comparative models of Zn-dependent 405-ADH I and Fe-dependent 405-ADH II showed 61.95% and 99.74% similarity to the crystal structures of LlAdhA from Lactococcus lactis and zmADH2 from Z. mobilis ZM4, respectively. Gas chromatography analysis showed that the transformants expressing ADH I and II produced ethanol at 2.5 and 3.9 % (v/v), respectively. Apparently, these two enzymes could function independently for bioethanol production in E. coli. The characteristics of ADH I and ADH II enzymes will be further investigated for the potential bioethanol production.
Alcohol dehydrogenase, ADH I, ADH II, bioethanol, Zymomonas mobilis
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