Sunday, July 29, 2007
P27

Substrate specificity of a galactose 6-phosphate isomerase from Lactococcus lactis that produces D-allose from D-psicose

Ha-Young Park1, Hye-Jung Kim1, Seon-Won Kim2, and Deok-Kun Oh1. (1) Department of Bioscience and biotechnology, Konkuk University, Seoul, South Korea, (2) Division of Applied Life Science, Gyeongsang National University, 900 Gajwadong, Jinju, 660-701, South Korea

We purified recombinant galactose 6-phosphate isomerase (LacAB) from Lactococcus lactis using HiTrap Q HP and Phenyl-Sepharose columns. The purified LacAB had a final specific activity of 1.79 units/mg. The molecular mass of native galactose 6-phosphate isomerase was estimated at 135.5 kDa using Sephacryl S-300 gel filtration, and the enzyme exists as a hetero-octamer of LacA and LacB subunits. The activity of galactose 6-phosphate isomerase was maximal at pH 7.0 and 30°C, and enzyme activity was independent of metal ions. When 100 g/L of d-psicose was used as the substrate, 25 g/L of d-allose and 13 g/L of d-altrose were simultaneously produced at pH 7.0 and 30°C after 12 h of incubation. The enzyme had broad specificity for various aldoses and ketoses. The interconversion of sugars with the same configuration except at the C2 position was driven by using a large amount of enzyme in extended reactions. The interconversion occurred via two isomerization reactions, i.e., the interconversion of d-allose↔d-psicose↔d-altrose.

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