Purification and properties of NAD+-dependent maltose dehydrogenase produced by alkalophilic Corynebacterium sp. No. 93-1.

NAD+-dependent maltose dehydrogenase was purified about 250-fold from the cell free extract of an alkalophilic Corynebacterium sp. No. 93-1. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis, sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and ultracentrifugation. The molecular weight of the enzyme was determined to be 40 000 +/- 2000 by gel filtration and SDS-polyacrylamide gel electrophoresis. The enzyme appeared to be a single peptide chain. The isoelectric point was pH 4.50. The optimal pH was 10.2. The enzyme was stable over the range of pH 6 to 10. NAD+-dependent maltose dehydrogenase showed very wide substrate specificity on monosaccharides, disaccharides and trisaccharides. Among these substrates, maltose was the most reactive. Also, the enzyme showed oxidative activity on maltotetraose and maltopentaose. The Km values at pH 10 were 2.1 mM for maltose and 0.15 mM for NAD+. It was conjectured that the primary product of this reaction was maltono-delta-lactone and its was hydrolyzed non-enzymatically to maltobionic acid. p-Chloromercuribenzoic acid, Hg2+ and Ag2+ completely inhibited the activity, and HADH also showed competitive inhibition on the activity.