The gene previously designated as putative c cyclodextrinase from Thermotoga maritima (TMG) was cloned and overexpressed in Escherichia coli. The recombinant TMG was partially purified and its enzymatic characteristics on various substrates were examined, The enzyme hydrolyzes various maltodextrins including maltotriose to maltoheptaose and cyclomaltodextrins (CDs) to mainly glucose and maltose. Although TMG could not degrade pullulan, it rapidly,. hydrolyzes acarbose, a strong amylase and glucosidase inhibitor. to acarviosine and glucose. Also, TMG initially hydrolyzes p-nitrophenyl-alpha-pentaoside to Live maltopentaose and p-nitrophenol, implying that the enzyme specifically cleaves a glucose unit from the reducing end of maltooligosaccharides unlike to other glucosidases. Since its enzymatic activity is negligible if a-methylglucoside is present in the reducing end, the type of the residue at the reducing end of the substrate is important for the TMG activity. These results Support the fact that TMG is a novel exo-acting glucosidase possessing the characteristics of both CD-/pullulan hydrolyzing enzyme and alpha-glucosidase. (C) 2002 Elsevier Science (USA). All rights reserved.