PURIFICATION AND SEQUENCE-ANALYSIS OF A NOVEL NADP(H)DEPENDENT TYPE-III ALCOHOL-DEHYDROGENASE FROM THERMOCOCCUS STRAIN AN1

An NADP(H)-dependent alcohol dehydrogenase was isolated from the hyper thermophilic archaeon Thermococcus strain AN1. This enzyme is a homote tramer with a subunit molecular weight of 46,700. The enzyme oxidizes a series of primary linear alcohols but not methanol. The pH and tempe rature optima with ethanol as the substrate are 6.8 to 7.0 and 85 degr ees C, respectively. The enzyme readily reduced acetaldehyde,vith NADP H as the cofactor. The gene encoding this enzyme has been cloned and s equenced. An open reading Game of 1,218 bp, starting with ATG and endi ng with TGA, was identified and corresponded to 406 amino acids. Seque nce comparisons show that this Thermococcus strain AN1 enzyme has sign ificant homologies,vith enzymes from the newly defined type III alcoho l dehydrogenase family. Thermococcus strain AN1 alcohol dehydrogenase is the first archaeal enzyme belonging to this family.