METABOLISM OF CYCLOHEXANE CARBOXYLIC-ACID BY THE PHOTOSYNTHETIC BACTERIUM RHODOPSEUDOMONAS-PALUSTRIS

Cyclohexane carboxylate supported relatively rapid growth (doubling ti mes 7-8 h) of Rhodopseudomonas palustris under oxic or photosynthetic conditions, but did not serve as a substrate for either of the known a romatic CoA ligases. A CoA ligase that thioesterifies cyclohexane carb oxylate was partially purified and did not cross react immunologically with the two CoA ligases purified previously from this bacterium. Cru de extracts of R. palustris cells grown with a range of aromatic or al icyclic acids contained a dehydrogenase that reacted with cyclohexane carboxyl-CoA or cyclohex-1-ene carboxyl-CoA, using 2,6-dichlorophenoli ndophenol or ferricenium ion as electron carrier. This activity was no t detected in extracts of adipate-, glutamate-, or succinate-grown cel ls. No oxidation or reduction of nonesterified cyclohexane carboxylate or cyclohexene carbocylate was detected in extracts of cells grown wi th aromatic or aliphatic substrates, neither aerobically nor anaerobic ally. A constitutively expressed thioesterase that hydrolyzed cyclohex ane carboxyl-CoA and also some alicyclic and aliphatic CoA derivatives was purified and characterized. The enzyme had little or no activity on benzoyl-CoA or 4-hydroxybenzoyl-CoA. The presence of a thioesterase that effectively hydrolyzes cyclohexane carboxyl-CoA suggests that tr ansient production of cyclohexane carboxylate is a physiological respo nse to temporary excess of reductant during metabolism of aromatic com pounds.