ANAEROBIC METABOLISM OF CYCLOHEX-1-ENE-1-CARBOXYLATE, A PROPOSED INTERMEDIATE OF BENZOATE DEGRADATION, BY RHODOPSEUDOMONAS-PALUSTRIS

Anaerobic benzoate degradation by the phototrophic bacterium Rhodopseu domonas palustris has been proposed to proceed via aromatic ring reduc tion reactions leading to cyclohex-1-ene-1-carboxyl-coenzyme A (CoA) f ormation. The alicyclic product is then proposed to undergo three beta -oxidation-like modifications resulting in ring cleavage. Illuminated suspensions of benzoate-grown cells converted [7-C-14] cyclohex-1-ene- 1-carboxylate to intermediates that comigrated with cyclohex-1-ene-1-c arboxyl-CoA, 2-hydrolcyclohexanecarboxyl-CoA, 2-ketocyclohexanecarboxy l-CoA, and pimelyl-CoA by thin-layer chromatography. This set of inter mediates was also formed by cells grown anaerobically or aerobically o n cyclohex-1-ene-1-carboxylate, indicating that benzoate-grown and cyc lohex-1-ene-1-carboxylate-grown cells degrade this alicyclic acid by t he same catabolic route. Pour enzymatic activities proposed to be requ ired for conversion of cyclohex-1-ene-1-carbolate to pimelyl CoA were detected at 3- to 10-fold-higher levels in benzoate-grown cells than i n succinate-grown cells. These were cyclohex-1-ene-1-carboxylate-CoA l igase, cyclohex-1-ene-1-carboxyl-CoA hydratase, 2-hydroxycyclohexaneca rboxyl-CoA dehydrogenase, and 2-ketocyclohexanecarboxyl-1-CoA hydrolas e (ring cleaving). Pimelyl-CoA was identified in hydrolase reaction mi xtures as the product of alicyclic ring cleavage. The results provide a first demonstration of an alicyclic ring cleavage activity.