Characterization of D-lactate dehydrogenase in Leuconostoc citreum KM20

Abstract

Objective: This study focused on investigating the enzymatic characteristics of D-lactate dehydrogenase (D-LDH) in Leuconostoc citreum KM20. Methods: The D-lactate dehydrogenase gene (LDH) from L.citreum KM20 was cloned and expressed to construct expression plasmid, and then transformed into Escherichia coli BL21 (DE3) for overexpression. Results: The enzymes encoded by LCK_00027 and LCK_00222 were purified by Ni-NTA column affinity chromatography with molecular mass of 40.0 kDa and 38.5 kDa, respectively. The specific activities were 2.18 U/mg and 153.10 U/mg, respectively. The optimal pH and temperature for pyruvate reduction were 8.0 and 40 ℃, respectively, while for the LCK_00222 encoding enzyme lactic acid oxidation the values were 12.0 and 30 ℃, respectively. The two enzymes had high activities toward oxaloacetic acid, sodium phenylpyruvate, and 2-oxoglutaric acid. Ca2+, Cu2+, and Na+ promoted the activity of the two enzymes, whereas Zn2+ and SDS inhibited. In addition, the Kcat/Km of LCK_00027 and LCK_00222 to pyruvate were 6.04×102 L/(mol·s) and 2.28×104 L/(mol·s), respectively. The Kcat/Km of LCK_00222 encoding enzyme to D-lactic acid was 65.0 L/(mol·s). Conclusion: D-LDH-1 and D-LDH-2 are key enzymes catalyzing the synthesis of D-lactic acid in Leuconostoc citrate.

Keywords

• gene engineering
• d-lactic
• d-lactate dehydrogenase
• leuconostoc citreum