A novel intracellular glucosyltransferase (GTase) was isolated from cells of Actinoplanes sp. CKD485-16-acarbose-producing cells. The enzyme was purified by DEAE-cellulose and G75-40 Sephadex chromatography. The molecular mass of the enzyme was estimated to be 62 kDa by SDS-polyacrylamide gel electrophoresis, and its isoelectric point (pI) was pH 4.3. The N-terminal sequence of the GTase consisted of NH2-Ser-Val-Pro-Leu-Ser-Leu-Pro-Ala-Glu-Trp. The optimum pH and temperature were 7.5 and 30degreesC. The enzyme was stable in a pH range of 5.5-9.0 and below 40degreesC. Enzymatic reactions were performed by incubating the GTase with various substrates. The GTase converted acarbose into component C, maltose into trehalose, and maltooligosaccharides into maltooligosyl trehaloses. The reactions were reversible. Various acarbose analogs were tested as inhibitors against the GTase as a means to suppress component C formation. Valienamine was the most potent, with an IC50 value of 2.4x10(-3) mM and showed a competitive inhibition mode.