ENZYMATIC-SYNTHESIS OF 3-DEOXY-D-MANNO-OCTULOSONATE 8-PHOSPHATE, 3-DEOXY-D-ALTRO-OCTULOSONATE 8-PHOSPHATE, 3,5-DIDEOXY-D-GLUCO(MANNO)-OCTULOSONATE 8-PHOSPHATE BY 3-DEOXY-D-ARABINO-HEPTULOSONATE 7-PHOSPHATE SYNTHASE

The phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphat e (DAH 7-P) synthase (phe), a key enzyme involved in the biosynthesis of the aromatic amino acid phenylalanine, expressed by the Escherichia coli gene aroG, which catalyzes the condensation of D-erythrose 4-pho sphate with phosphoenolpyruvate (PEP) to give DAH 7-P, was cloned into the expression vector pT7-7 for overexpression in E. coil. Purified e nzyme from this expression system was used to demonstrate that DAH 7-P synthase (phe) also catalyses the aldol-type condensation of PEP with the 5-carbon analogues D-arabinose 5-phosphate, D-ribose 5-phosphate, and 2-deoxy-D-ribose 5-phosphate to yield 3-deoxy-D-manno-octulosonat e 8-phosphate, 3-deoxy-D-altro-octulosonate 8-phosphate, and 3,5-dideo xy-D-gluco(manno)-octulosonate 8-phosphate, respectively, as determine d by H-1 NMR and other standard analytical methods. The kinetic parame ters, K-m and V-max, for these reactions were determined. The 3- and 6 -carbon phosphorylated monosaccharides, D,L-glyceraldehyde 3-phosphate and D-glucose 6-phosphate, as well as the nonphosphorylated 5-carbon analogues D-arabinose 5-phosphate, D-ribose 5-phosphate, and 2-deoxy-D -ribose 5-phosphate were not substrates.