Abstract
NADP-dependent gluconate 5-dehydrogenase catalyzes the reversible oxidoreduction reaction between D-gluconate and 5-keto-D-gluconate. NADP-dependent gluconate 5-dehydrogenase from bacteria and fungi has been reported. The reported enzyme showed activity only for NADP as the cofactor. This study purified and characterized a NAD(P)-dependent gluconate 5-dehydrogenase (TmGNDH) from the archaea Thermotoga maritima MSB8. TmGNDH is composed of two identical subunits, and a single subunit has 255 amino acids with molecular mass of 28 kDa. TmGNDH is affiliated with the short-chain dehydrogenase/reductase family. Purified TmGNDH has a specific activity of 102.8 U/mg. The enzyme preferred NADP to NAD as its cofactor. TmGNDH exhibited a Km value of 121.3 ± 3.0 mM and k_cat value of 3181 ± 34.1 s^(-1) toward D-gluconate as a substrate. TmGNDH had lower activity with D-sorbitol, D-xylitol, D-glucose and D-xylose as substrates. The optimal pH and temperature of TmGNDH were observed at pH 9.0 and 60℃ with NADP as the cofactor. The thermostability of the enzyme suggests that it can be used as an industrially effective tool for synthesizing 5-keto-D-gluconate.
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