Biochemistry

Recovering Carbon and Nitrogen

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Science  15 Oct 2010:
Vol. 330, Issue 6002, pp. 296
DOI: 10.1126/science.330.6002.296-a
CREDIT: RAMAZZINA ET AL., NAT. CHEM. BIOL. 6, 10.1038/NCHEMBIO.445 (2010)

Purine nucleotide biosynthesis, critical for the assembly of DNA and RNA, uses amino acid precursors and requires energy. In general, however, purine breakdown (catabolism) does not generate energy, nor do most organisms have the capacity to reincorporate very many of the constituent carbon and nitrogen atoms into productive pathways toward other essential biomolecules. In fact, the catabolic intermediate uric acid can cause kidney disease in humans, and the end product glyoxylate can be harmful, too. Metazoa have a glyoxylate detoxification system in which alanine-glyoxylate aminotransferase (AGXT) converts glyoxylate to glycine at the expense of alanine. In contrast, Bacillus fastidiosus (a facultative aerobe found in soil and in the animal gut) thrives on purine degradation intermediates. Ramazzina et al. show that B. subtilis PucG protein is an enzyme with structural similarity to human AGXT1. Instead of consuming alanine, it catalyzes a transamination between S-ureidoglycine (carbons in green at right), which is an unstable intermediate in purine metabolism, and glyoxylate to give oxalurate and glycine. Although the original function of UGXT may have been glyoxylate detoxification, its willingness to use keto acids as amino group acceptors enables the recycling of the carbon and nitrogen atoms of purines.

Nat. Chem. Biol. 6, 10.1038/nchembio.445 (2010).

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