Correlation between kinetic and thermodynamic stability. Half-lives were measured in DM at 1.7 mg/ml where the reaction approximates first-order kinetics. The relative half-life is the half-life of the mutant divided by the half-life of the wild-type protein. [SDS]1/2 is the SDS concentration at the midpoint of the second phase of the SDS denaturation curves and taken as the point of maximum slope. In addition to the wild-type protein, data are shown for cysteine substitution mutants at the following sixteen positions: 46, 47, 53, 54, 55, 56, 57, 59, 60, 61, 62, 63, 64, 66, 68, and 70.