A constitutive extracellular alpha-glucosidase from Chaetomium thermophilum var. coprophilum was purified and characterised. The enzyme exhibited a carbohydrate content of 14% and an apparent molecular mass of 107 kDa. estimated by gel filtration. Analysis by SDS-PAGE revealed two polypeptide bands of 22 and 26 kDa, suggesting that the enzyme was constituted of two subunits of 22 kDa and two subunits of 26 kDa. Optima of pH and temperature were 7.0 and 60 degrees C, respectively. The enzyme hydrolysed maltose, amylose, starch, maltooligosaccharides and isomaltose, in order of preference. The enzyme exhibited transglycosylation activity producing trehalose and maltooligosaccharides from 5% maltose. At early stages of the transglycosylation reaction trehalose was the predominant product: at later stages maltooligosaccharides were also accumulated. Trehalose inhibited both glycosyl hydrolase and transglycosylase activities. To our knowledge this is the first report of a alpha-glucosidase from a filamentous fungus that in addition to glycosyl hydrolase activity produces trehalose by transglycosylation. (c) 2006 Elsevier Ltd. All rights reserved.