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영어
The uncharacterized gene previously proposed as a mannose-6-phosphate isomerase from Geobacillus thermodenitrificans was cloned and expressed in E scherichia coli. The maximal activity of the recombinant enzyme was observed at pH 7.0 and 70ºC in the presence of 1 mM Co2+. The isomerization activity was specific for aldose substrates possessing hydroxyl groups oriented in the same direction at the C2 and C3 positions,such as the D- and L-forms of ribose, lyxose, talose, mannose, and allose. The enzyme exhibited the highest activity for L-ribulose among all pentoses and hexoses. Thus, L-ribose, as a potential starting material for many L-nucleoside-based pharmaceutical compounds, was produced at 213 g/liter from 300 g/liter L-ribulose by mannose-6-phosphate isomerase at 70ºC for 3 h, with a conversion yield of 71 % and a volumetric productivity of 71 g liter–1 h–1. Two enzymes of L-arabinose isomerase and mannose-6-phosphate isomerase from G. thermodenitrificans produced 118 g/liter L-ribose from 500 g/liter L-arabinose at pH 7.0, 70ºC, and 1 mM Co2+ for 3 h, with a conversion yield of 23.6 % and a volumetric productivity of 39.3 g liter–1 h–1.