Heterologous Expression and Characterization of an Alcohol Dehydrogenase from the Archeon Thermoplasma acidophilum

Analysis of the Thermoplasma acidophilum DSM 1728 genome identified two putative alcohol dehydrogenase (ADH) open reading frames showing 50.4% identity against each other. The corresponding genes Ta0841 and Ta1316 encode proteins of 336 and 328 amino acids with molecular masses of 36.48 and 36.01 kDa, respectively. The genes were expressed in Escherichia coli and the recombinant enzymes were functionally assessed for activity. Throughout the study only Ta1316 ADH resulted active in the oxidative reaction in the pH range 28 (optimal pH 5.0) and temperatures from 25 to 90 degrees C (optimal 75 degrees C). This ADH catalyzes the oxidation of several alcohols such as ethanol, methanol, 2-propanol, butanol, and pentanol during the reduction of the cofactor NAD(+). The highest activity was found in the presence of ethanol producing optically pure acetaldehyde. The specific enzyme activity of the purified Ta1316 ADH with ethanol as a substrate in the optimal conditions was 628.7 U/mg.