Stereochemistry of 3-deoxyoctulosonate 8-phosphate synthase.
(Z)- and (E)-[3-2H]phosphoenolpyruvate were prepared chemically by the reductive deuteration of (Z)- and (E)-3-bromophosphoenolpyruvate, respectively, and were converted into 3-deoxyoctulosonate 8-phosphates deuterated at the C-3 position by incubation with unlabeled D-arabinose 5-phosphate in the presence of the enzyme, 3-deoxyoctulosonate 8-phosphate synthase (EC4.1.2.16) purified from Escherichia coli K-12 containing the plasmid pMW101. Analysis of the stereochemistry of the two 3-deoxyoctulosonate 8-phosphates deuterated at the C-3 position by 1H NMR showed that the (Z)-[3-2H]phosphoenolpyruvate had produced [3-2H]-3-deoxyoctulosonate 8-phosphate of predominantly the 3S configuration and that the E isomer had given predominantly (3R)-[3-2H]-3-deoxyoctulosonate 8-phosphate. The 3-deoxyoctulosonate 8-phosphate synthase reaction is therefore stereospecific with respect to the C-3 of phosphoenolpyruvate. The results indicate a si face attack from the C-3 of phosphoenolpyruvate, a result identical to that reported for 3-deoxyheptulosonate 7-phosphate synthase (EC 4.1.2.15), an enzyme catalyzing an identical aldol-type condensation, except that it takes place between phosphoenolpyruvate and D-erythrose 4-phosphate. The stereochemistry with respect to the face of the carbonyl of the attacked aldehyde, in both 3-deoxyoctulosonate 8-phosphate synthase and 3-deoxyheptulosonate 7-phosphate synthase, is re. On the basis of the results of the studies reported herein, the presence of a transient methyl group at the C-3 of phosphoenolpyruvate as part of the reaction mechanism seems unlikely.
Dotson
G D
GD
Interdepartmental Program in Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor 48109-1065.
Nanjappan
P
P
Reily
M D
MD
Woodard
R W
RW
D000446:Aldehyde-Lyases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D009682:Magnetic Resonance Spectroscopy; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011994:Recombinant Proteins; D013237:Stereoisomerism; D013379:Substrate Specificity; D013400:Sugar Acids / Q000737:chemistry* / Q000378:metabolism
D011994:Recombinant Proteins; D013400:Sugar Acids; C002532:2-keto-3-deoxyoctonate; D010728:Phosphoenolpyruvate; C020011:2-dehydro-3-deoxyphosphooctonate aldolase; D000446:Aldehyde-Lyases