Figure 3. Modified Kitz-Wilson plot for GRx1 inactivation by sporidesmin.

GRx1 (0.9 μM) was incubated with different concentrations of sporidesmin (0.05–1 mM) for 5 min at 30 °C, 0.1 M K phosphate, pH 7.5, and residual activities were determined relative to ethanol treated control as described in Figure 2. K_I and k_inact were determined according to the relationship: ln (E_o/E_t)/ t = k_inact [I] / (K_I + [I]), where E_o and E_t refer to GRx1 concentrations at times 0 and t, [I] refers to sporidesmin concentration, K_I is the concentration of inactivator that gives half the maximal rate of inactivation, and k_inact is the net rate constant for inactivation. The K_I of sporidesmin for GRx1 is 0.15 mM and the k_inact is 0.72 min⁻¹. Each point represents the mean value, plus and minus the standard error, for at least three determinations. Where error bars are not evident they are within the size of the symbol.