Abstract
Abstract d -Mannose is the aldose isomer of d -fructose and displays unique physiological functions and health applications. As a result, it has attracted increasing interest from the public. Because of its wide substrate specificity, d -lyxose isomerase (D-LI) has been applied to d -mannose bioproduction. In this article, the Thermoflavimicrobium dichotomicum D-LI encoding gene was cloned and overexpressed in Escherichia coli BL21(DE3). The novel protein T. dichotomicum D-LI was identified and characterized, and its maximum enzyme activity was exhibited at pH 7.5 (phosphate buffer) and 60 °C in the presence of Mn2+. Similar to other D-LIs, T. dichotomicum D-LI formed a homodimeric structure and showed strict conservation of the metal coordination and substrate binding sites. The D-LI half-life (t1/2) was 9.91 h and 3.05 h at 55 and 60 °C, respectively, and its melting temperature (Tm) was 72.85 °C. T. dichotomicum D-LI displayed the highest specific activity towards d -lyxose among the substrates tested, followed by d -mannose. It also efficiently converted d -fructose to d -mannose, and the equilibrium ratio between d -mannose and d -fructose during T. dichotomicum D-LI activity was 25:75. From 500 g/L d -fructose, 110.5 g/L d -mannose was produced after 6 h, suggesting that T. dichotomicum D-LI might provide an alternative for d -mannose production.
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