Figure 2: Yeast cell biocatalytic activity is dependent on the substrate concentration. A. Specific activity of the intact yeast biocatalyst is dependent on the organophosphate substrate concentration. S308L-OPH yeast was incubated in the presence of differing demeton-S methyl concentrations at 30°C. The numbers represent the mean specific activity (μmoles hydrolyzed/ min/OD600 of 1) of three independent cultures ± SD. B. Yeast biocatalyticmediated demeton-S methyl detoxification measured by the reduced ability of the organophosphate to inhibit AChE activity. Hydrolysis assays with 50 μM or 250 μM demeton-S methyl were performed with control yeast (no OPH), wild-type yeast (OPH) or S308L-OPH yeast. After varying incubation periods at 30°C, the ability of demeton-S methyl to inhibit AChE was measured. The S308L-OPH mediated reduction in AChE activity was directly indicative of the reduced toxicity of the agent. Readings represent the mean ± SD of three independent cultures.