Abstract
NADP-dependent maltose dehydrogenase (NADP-MalDH) was completely purified from the cell free extract of alkalophilic Corynebacterium sp. No. 93-1. The molecular weight of the enzyme was estimated as 45, 000_??_48, 000. The enzyme did not have a subunit structure. The isoelectric point of the enzyme was estimated as pH 4.48. The pH optimum of the enzyme activity was pH 10.2, and it was stable at pH 6 to 8. The temperature optimum was 40°C, and the enzyme was slightly protected from heat inactivation by 1mM NADP. The enzyme oxidized D-xylose, maltose and maltotriose, and the Km values for these substrates were 150mM, 250mM and 270mM, respectively. Maltotetraose and maltopentaose were suitable substrates. The Km value for NADP was 1.5mM with 100mM maltose as substrate. The primary product of this reaction from maltose was estimated as maltono-b-lactone, and it was hydrolyzed non-enzymatically to maltobionic acid. The enzyme was inhibited completely by PCMB, Ag+ and Hg2+.
