2-Hydroxycyclohexanecarboxyl coenzyme A dehydrogenase, an enzyme characteristic of the anaerobic benzoate degradation pathway used by Rhodopseudomonas palustris

J Bacteriol. 2000 May;182(10):2753-60. doi: 10.1128/JB.182.10.2753-2760.2000.


A gene, badH, whose predicted product is a member of the short-chain dehydrogenase/reductase family of enzymes, was recently discovered during studies of anaerobic benzoate degradation by the photoheterotrophic bacterium Rhodopseudomonas palustris. Purified histidine-tagged BadH protein catalyzed the oxidation of 2-hydroxycyclohexanecarboxyl coenzyme A (2-hydroxychc-CoA) to 2-ketocyclohexanecarboxyl-CoA. These compounds are proposed intermediates of a series of three reactions that are shared by the pathways of cyclohexanecarboxylate and benzoate degradation used by R. palustris. The 2-hydroxychc-CoA dehydrogenase activity encoded by badH was dependent on the presence of NAD(+); no activity was detected with NADP(+) as a cofactor. The dehydrogenase activity was not sensitive to oxygen. The enzyme has apparent K(m) values of 10 and 200 microM for 2-hydroxychc-CoA and NAD(+), respectively. Western blot analysis with antisera raised against purified His-BadH identified a 27-kDa protein that was present in benzoate- and cyclohexanecarboxylate-grown but not in succinate-grown R. palustris cell extracts. The active form of the enzyme is a homotetramer. badH was determined to be the first gene in an operon, termed the cyclohexanecarboxylate degradation operon, containing genes required for both benzoate and cyclohexanecarboxylate degradation. A nonpolar R. palustris badH mutant was unable to grow on benzoate or cyclohexanecarboxylate but had wild-type growth rates on succinate. Cells blocked in expression of the entire cyclohexanecarboxylate degradation operon excreted cyclohex-1-ene-1-carboxylate into the growth medium when given benzoate. This confirms that cyclohex-1-ene-1-carboxyl-CoA is an intermediate of anaerobic benzoate degradation by R. palustris. This compound had previously been shown not to be formed by Thauera aromatica, a denitrifying bacterium that degrades benzoate by a pathway that is slightly different from the R. palustris pathway. 2-Hydroxychc-CoA dehydrogenase does not participate in anaerobic benzoate degradation by T. aromatica and thus may serve as a useful indicator of an R. palustris-type benzoate degradation pathway.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alcohol Oxidoreductases / genetics
  • Alcohol Oxidoreductases / metabolism*
  • Amino Acid Sequence
  • Anaerobiosis
  • Animals
  • Base Sequence
  • Benzoates / metabolism*
  • Cyclohexanecarboxylic Acids / metabolism
  • DNA, Bacterial
  • Genes, Bacterial
  • Molecular Sequence Data
  • Mutagenesis
  • Operon
  • Rabbits
  • Rhodopseudomonas / enzymology*
  • Rhodopseudomonas / genetics
  • Sequence Homology, Amino Acid


  • Benzoates
  • Cyclohexanecarboxylic Acids
  • DNA, Bacterial
  • Alcohol Oxidoreductases
  • 2-hydroxycyclohexanecarboxyl Coenzyme A dehdrogenase