Effect of herbicide tralkoxydim and 2-acylcyclohexane-1,3-diones on peroxidase activity

Effect of 2-acylcyclohexane-1,3-dione derivatives (tralkoxydim and its diketone precursors) on peroxidase-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), o-phenylenediamine (PDA), and the phenol-4-aminoantipyrine (4-AAP) couple has been studied. This effect varies from horseradish peroxidase (HRP) inactivation to activation in the reactions of peroxidation ofTMB, PDA, and, to a lesser extent, the phenol-4-AAP couple. The diketone-mediated HRP activation depends strongly on pH, presence of dimethylformamide, the structures of tralkoxydim and other diketones, and the substrate nature. The type of activation in the course of peroxidation with the presence of tralkoxydim can be noncompetitive (PDA and TMB) or mixed (TMB) depending on conditions. The maximal level of the HRP activation mediated by diketones depends on their structure. It can reach 4000% of the initial HRP-catalyzed peroxidation rate for TMB and ca. 1000% for PDA. A test system is proposed for quantitative tralkoxydim assay at millimolar concentration. It includes HRP and TMB as the substrate with spectrometrical monitoring of the TMB peroxidation product at 655 nm.