Journal of Bacteriology, January 2001, p. 1-11, Vol. 183, No. 1
Department of Chemistry, University of Utah,
Salt Lake City, Utah 84112
Received 22 May 2000/Accepted 24 August 2000
In eubacteria, green algae, and plant chloroplasts, isopentenyl
diphosphate, a key intermediate in the biosynthesis of
isoprenoids, is synthesized by the methylerythritol phosphate pathway.
The five carbons of the basic isoprenoid unit are assembled by
joining pyruvate and D-glyceraldehyde 3-phosphate. The
reaction is catalyzed by the thiamine diphosphate-dependent enzyme
1-deoxy-D-xylulose 5-phosphate synthase. In
Rhodobacter capsulatus, two open reading frames (ORFs) carry the genes that encode
1-deoxy-D-xylulose 5-phosphate synthase. ORF 2816 is
located in the photosynthesis-related gene cluster, along with most of
the genes required for synthesis of the photosynthetic machinery of the
bacterium, whereas ORF 2895 is located elsewhere in the
genome. The proteins encoded by ORF 2816 and ORF 2895, 1-deoxy-D-xylulose 5-phosphate synthase A and B, containing
a His6 tag, were synthesized in Escherichia
coli and purified to greater than 95% homogeneity in two steps.
1-Deoxy-D-xylulose 5-phosphate synthase A appears to be a
homodimer with 68 kDa subunits. A new assay was
developed, and the following steady-state kinetic constants were
determined for 1-deoxy-D-xylulose 5-phosphate synthase A
and B: Kmpyruvate = 0.61 and
3.0 mM, KmD-glyceraldehyde
3-phosphate = 150 and 120 µM, and
Vmax = 1.9 and 1.4 µmol/min/mg in 200 mM sodium citrate (pH 7.4). The ORF encoding
1-deoxy-D-xylulose 5-phosphate synthase B complemented the
disrupted essential dxs gene in E. coli strain FH11.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.1-11.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
1-Deoxy-D-Xylulose 5-Phosphate Synthase, the Gene
Product of Open Reading Frame (ORF) 2816 and ORF 2895 in
Rhodobacter capsulatus

*
Corresponding author. Mailing address: Department of
Chemistry, University of Utah, Salt Lake City, UT 84112. Phone: (801) 581-6685. Fax: (801) 581-4391. E-mail:
poulter{at}chemistry.utah.edu.
Present address: Maui Agricultural Research Center, University of
Hawaii, Kula, HI 96790.
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