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Journal of Bacteriology, October 2000, p. 5332-5341, Vol. 182, No. 19
Department of Molecular and Cell Biology, The
University of Texas at Dallas, Richardson, Texas 75083-0688
Received 20 March 2000/Accepted 4 July 2000
Escherichia coli is not known to utilize purines, other
than adenine and adenosine, as nitrogen sources. We reinvestigated purine catabolism because a computer analysis suggested several potential
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Purine Catabolism in Escherichia coli
and Function of Xanthine Dehydrogenase in Purine Salvage

and
54-dependent promoters within a 23-gene
cluster whose products have homology to purine catabolic enzymes. Our
results did not provide conclusive evidence that the
54-dependent promoters are active. Nonetheless, our
results suggest that some of the genes are metabolically significant.
We found that even though several purines did not support growth as the sole nitrogen source, they did stimulate growth with aspartate as the
nitrogen source. Cells produced 14CO2 from
minimal medium containing [14C]adenine, which implies
allantoin production. However, neither ammonia nor carbamoyl phosphate
was produced, which implies that purine catabolism is incomplete and
does not provide nitrogen during nitrogen-limited growth. We
constructed strains with deletions of two genes whose products might
catalyze the first reaction of purine catabolism. Deletion of one
eliminated 14CO2 production from
[14C]adenine, which implies that its product is necessary
for xanthine dehydrogenase activity. We changed the name of this gene
to xdhA. The xdhA mutant grew faster with
aspartate as a nitrogen source. The mutant also exhibited sensitivity
to adenine, which guanosine partially reversed. Adenine sensitivity has
been previously associated with defective purine salvage resulting from
impaired synthesis of guanine nucleotides from adenine. We propose that
xanthine dehydrogenase contributes to this purine interconversion.
*
Corresponding author. Mailing address: Department of
Molecular and Cell Biology, Mail Station FO 3.1, The University of
Texas at Dallas, P.O. Box 830688, Richardson, TX 75083-0688. Phone: (972) 883-2502/2523. Fax: (972) 883-2409. E-mail:
reitzer{at}utdallas.edu.
Present address: Cereon Genomics, Cambridge, MA 02139.
Present address: Department of Biology, University of California
at San Diego, La Jolla, CA 92093-0116.
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