Evidence that phenol phosphorylation to phenylphosphate is the first step in anaerobic phenol metabolism in a denitrifying Pseudomonas sp.

Abstract

Anaerobic phenol degradation has been shown to proceed via carboxylation of phenol to 4-hydroxybenzoate. However, in vitro the carboxylating enzyme was inactive with phenol; only phenylphosphate (phosphoric acid monophenyl ester) was readily carboxylated. We demonstrate in a denitrifying Pseudomonas strain that phenylphosphate is the first detectable product formed from phenol in whole cells and that subsequent phenylphosphate consumption parallels 4-hydroxybenzoate formation. These kinetics are consistent with phosphorylation being the first step in anaerobic phenol degradation. Various cosubstrates failed so far to act as phosphoryl donor for net phosphorylation of phenol in cell extracts. Yet, cells anaerobically grown with phenol contained an enzyme that catalyzed an isotope exchange between [U-14C]phenol and phenylphosphate. This transphosphorylation activity was anaerobically induced by phenol but was stable under aerobic conditions and required Mn2+ and polyethylene glycol. Activity was optimal at pH 5.5 and half-maximal with 0.6 mM Mn2+, 0.2 mM phenylphosphate, and 1 mM phenol. It is proposed that the phenol exchange/transphosphorylation reaction is catalyzed as partial reaction by an inducible phenol phosphorylating enzyme. The isotope exchange demands that a phosphorylated enzyme was formed in the course of the reaction, which might be similar to the phosphotransferase system of sugar transport.