BIOCATALYTIC SYNTHESIS OF AROMATICS FROM D-GLUCOSE - THE ROLE OF TRANSKETOLASE

The percentage of D-glucose that microbes such as Escherichia coli convert into aromatics is one of the key considerations that will determine the long-term utility of such biocatalytic syntheses. Considerable research has focused on improving percent conversions by increasing the in vivo catalytic activity of the first enzyme involved in aromatic biosynthesis, 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) synthase. This report details a different strategy based on increasing the in vivo catalytic activity of the enzyme transketolase when DAHP synthase catalytic activity is amplified. A genetic locus (tkt) encoding transketolase was used to vary the catalytic activity of transketolase in E. coli. The catalytic activity of DAHP synthase was manipulated with an aroG gene encoding an isozyme of DAHP synthase that was insensitive to feedback inhibition. Increases in DAHP synthase catalytic activity ultimately reached a point where no further improvements in aromatic biosynthesis were observed. At this limiting level of aromatic biosynthesis, amplification of transketolase catalytic levels achieved an additional 2-fold increase in the percentage of D-glucose siphoned into aromatic biosynthesis.