Experimental and theoretical affinity studies of substituted phenols to chlorocatechol 1,2-dioxygenases: A step toward the comprehension of inhibitor/substrate binding to intradiol dioxygenases

The inhibition kinetics of 4- and 3-chlorocatechol 1,2-dioxygenases from Rhodococcus opacus 1CP were investigated using 14 different substituted phenols. The obtained experimental data were analyzed against experimental (pKa) and theoretical reactivity parameters of the phenols calculated by semi-empirical AM1 method (DPE, EHOMO, charge on oxygen atom of the reactive hydroxyl group, van der Waals surface areas and partial charges of substituents on aromatic ring). From these comparisons it appears that the main factor determining the inhibitors binding in the active center of these enzymes is the deprotonation ability of their reactive hydroxyl group. The analysis also allowed to detect, in 3-CCD, enzyme factors influencing on the interactions with the investigated phenols. Some correlations between the calculated van der Waals surface areas as well as the partial charges of substituents on the aromatic ring of the phenols and their inhibition effect on the enzymes were found.