Enzyme activity remaining with respect to control (no inhibitor) after 10 min incubation of RLM biocolloids, NADPH generating system with: a) different concentrations of KET in the presence of 0.1 mM NNK(open circle, dashed line) and 1.0mM NNK (closed squares, full line) b) different concentrations of 4-MEP in the presence of 0.1 mM NPYR (half closed squares, dashed line) and 1.0mM NPYR(closed circle, full line)