17] Alcohol dehydrogenase from Thermococcus strain AN1

Abstract

Thermococcus strain AN1 is an extremely thermophilic, obligately anaerobic, sulfur-metabolizing archaeon of the order Thermococcales . The organism was isolated from a thermal pool at Kuirau Park, Rototua, New Zealand. It grows within the temperature range of 55° to 92° with optimum growth between 75° and 80° and at pH values ranging from 5.4 to 9.0 with optimum growth at pH 7.4. Alcohol dehydrogenases (ADHs) are widely distributed in nature. They display a wide range of substrate specificity with enzymes that utilize short-chain primary alcohols and pyridine nucleotides as coenzymes being the best studied. Alcohol dehydrogenase from Thermococcus AN1 is classified as a type III ADH based on its gene sequence. Type III ADHs show a high degree of sequence similarity within the family. They have 32 highly conserved residues, including six proline and eight glycine residues, which suggests possible similarities in their threedimensional structures). They also have a 15 amino acid sequence containing three conserved histidine residues; two are located in an α-helix, are implicated in metal binding, and thus are likely involved with the catalytic mechanism of the enzyme. Studies of the physiological roles of ADHs in the obligately fermentative and ethanologenic bacterium Z. mobilis have revealed that type III ADH is an abundant isozyme with a high specificity for ethanol as a substrate.