FIGURE 5.
Reaction of wild-type ALAS and the Ser-254 variants (5 μm) with ALA. The observed rate constants were calculated by fitting the decrease in intrinsic protein fluorescence over time to Equation 2 for a single exponential process. A, resolved equilibrium and rate constants for wild-type ALAS are as follows: KD = 500 ± 16 μm, k1 = 0.120 ± 0.015 s−1, and k−1 = 0.140 ± 0.05 s−1. B, for the S254A variant, the constants are as follows: KD = 855 ± 66 μm, k1 = 0.235 ± 0.006 s−1, and k−1 = 0.29 ± 0.02 s−1. C, for the S254T variant, the constants are as follows: KD = 832 ± 49 μm, k1 = 0.19 ± 0.09 s−1, and k−1 = 0.057 ± 0.007 s−1.