Comparison of substituted 2-nitrophenol degradation by enzyme extracts and intact cells

Abstract

The first catabolic pathway enzyme, nitrophenol oxygenase, transforms o-nitrophenol (ONP) to catechol. Thirteen of 16 substituted nitrophenols tested were actively transformed by both enzyme preparations and intact cells yielding a wide range of K_m (K_s) and V_max. Individual chemicals in binary mixtures demonstrated competitive inhibition. Chemical and physical characteristics (electron withdrawal, size, and position of substitution on the 2-nitrophenol ring) affected degradation kinetics. The strongest correlations were between K_m or V_max values and electron withdrawal, though there was also evidence for effects relating to position and size of substitution on the aromatic ring. Kinetic parameters determined for enzyme preparations did not correlate to those determined for intact cells. Though enzyme reactivity ultimately determined whether a given chemical would be transformed, the transformation by intact cells was apparently affected by factors other than those directly impacting the initial catabolic enzyme.