Biochemical characterization of the HpxO enzyme from Klebsiella pneumoniae, a novel FAD-dependent urate oxidase

Biochemistry. 2009 Apr 14;48(14):3033-5. doi: 10.1021/bi900160b.


The HpxO enzyme from Klebsiella pneumoniae was recently proposed, on the basis of genetic studies, to catalyze the hydroxylation of uric acid to 5-hydroxyisourate as part of the purine catabolic pathway. Its primary sequence suggests that the HpxO catalytic activity depends on a flavin cofactor (FAD), contrasting with all previously studied urate oxidase enzymes, which have no cofactor requirement. Here we demonstrate biochemically that HpxO is an FAD-dependent urate oxidase. Our data are consistent with the proposal that HpxO-bound flavin hydroperoxide is the hydroxylating species. These results confirm the existence of a novel mechanistic paradigm in purine catabolism.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Flavin-Adenine Dinucleotide*
  • Hydroxylation
  • Klebsiella pneumoniae / enzymology*
  • Purines / metabolism
  • Urate Oxidase / chemistry*
  • Urate Oxidase / metabolism
  • Uric Acid / analogs & derivatives
  • Uric Acid / metabolism


  • 5-hydroxyisourate
  • Purines
  • Flavin-Adenine Dinucleotide
  • Uric Acid
  • Urate Oxidase