Wang Jianhua

Expression, purification and characterization of a quinoprotein L-sorbose dehydrogenase from Ketogulonicigenium vulgare Y25

It is well known thatxa0Ketogulonicigenium vulgarexa0Y25 could effectively oxidize L-sorbose to 2-keto-L-gulonic acid (2KGA), an industrial precursor of vitamin C. There in, L-sorbose dehydrogenase is one of the key enzymes responsible for the production of 2KGA. From this organism, the coding region ofxa0sdhxa0gene was cloned into pET22b plasmid and its transcription product was overexpressed. This procedure allowed purification of L-sorbose dehydrogenase and production of polyclonal antibodies. In Western blot assays, the antibodies gave a positive reaction against bacteria protein extract and purified L-sorbose dehydrogenase. The molecular mass of the enzyme was 60532 Da, and the N-terminal amino acid sequence was determined to be QTAIT. The Native-PAGE and resting-cell reaction assay showed that purified L-sorbose dehydrogenase could convert L-sorbose to 2KGA, and PQQ was found to be indispensable for its activity as prosthetic group. The enzyme showed broad substrates specificity and thexa0Kmxa0value for L-sorbose and 1-propanol was 21.9 mM and 0.13 mM, respectively. The optimum pH of the enzyme activity was 8.0, and the optimum temperature was 35°C. The activity of the L-sorbose dehydrogenase was greatly stimulated by Ca2+xa0and strongly inhibited by Co2+xa0and Cu2+. The results obtained from the present study showed that a PQQ-dependent L-sorbose dehydrogenase could oxidize L-sorbose into 2-keto-L-gulonic acidxa0in vitro. n n xa0 n n Key words:xa0Ketogulonicigenium vulgare,xa02-keto-L-gulonic acid,xa0L-sorbose dehydrogenase, quinoprotein.