代谢
好氧条件下，苯酚的降解通常通过苯酚羧化为4-羟基苯甲酸进行。然而，在体外实验中，羧化酶对苯酚不起作用；只有苯基磷酸（单苯基磷酸）能够被轻易羧化。我们在一种反硝化假单胞菌菌株中证明，苯基磷酸是整个细胞中从苯酚形成的第一个可检测到的产物，随后苯基磷酸的消耗与4-羟基苯甲酸的形成平行。这些动力学特征与磷酸化是厌氧苯酚降解的第一步相一致。到目前为止，各种共同底物未能作为磷酸化苯酚的磷酸供体。然而，用苯酚厌氧生长的细胞含有一个酶，该酶催化了[U-14C]苯酚和苯基磷酸之间的同位素交换。这种转磷酸化活性是由苯酚在厌氧条件下诱导的，但在好氧条件下是稳定的，并且需要Mn2+和聚乙二醇。该活性在pH 5.5时达到最佳，当Mn2+为0.6 mM、苯基磷酸为0.2 mM和苯酚为1 mM时，活性为最大值的一半。推测苯酚交换/转磷酸化反应是由一种可诱导的苯酚磷酸化酶作为部分反应催化的。同位素交换要求在反应过程中形成了一种磷酸化酶，这可能与糖运输的磷酸转移酶系统相似。
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.
来源:Hazardous Substances Data Bank (HSDB)
