Characterization of a D-psicose 3-epimerase from Dorea sp CAG317 with an acidic pH optimum and a high specific activity

Ketose 3-epimerase displayed an important role in not only the cyclic monosaccharides bioconversion strategy, named lzumoring, but also in the industrial biological production of D-psicose, a novel low-calorie rare sugar widely used in food and medical industries. Since the non-enzymatic side reactions could be reduced in acid conditions, slightly acidic pH optimum is one of the main issues for biological production of D-psicose. In this study, we first characterized an acidic ketose 3-epimerase, the recombinant D-psicose 3-epimerase (DPEase) from Dorea sp. CAG317. The protein exhibited high amino acid sequence identity with other reported DPEases, and was determined as a homotetramer with subunit molecular weight approximately 33 kDa, which was the same as other reported findings. The recombinant DPEase was a metal-dependent enzyme with the optimum metal cofactor as Co2+. In presence of 1 mM of Co2+, the enzyme displayed the maximal activity as 803 U/mg at pH 6.0 and 70 degrees C. The catalytic efficiency (k(cat)/K-m) was measured to be 412 and 199 mM(-1) min(-1) toward D-psicose and D-fructose, respectively. The equilibrium ratio between D-fructose and D-psicose was approximately 30:70, and the elevated temperature did not significantly shift the equilibrium toward D-psicose. Compared to other reported DPEases, the recombinant Dorea sp. DPEase displayed significantly higher specific activity at acidic pHs and remarkably higher productivity of D-psicose at pH 6.0, indicating that it was appropriate for use as a new source of D-psicose producing enzyme. (C) 2015 Elsevier B.V. All rights reserved.