Effect of ionic strength on the high-spin content in the 1-PB-bound P450eryF wild-type, its mutants, and labeled derivatives. (a) Data obtained with the wild-type enzyme (○), S93C (•), C154S (▵), C154A (▴), S93C/C154S (□), and S93C/C154A (▪). (b) Results of the experiments with S93C/C154S labeled with CPM (•), MDCC (▪), and mBBr (♦). The curves characterizing P450eryF wild-type (○) and its unlabeled S93C/C154S mutant (□) are also shown in this panel for comparison. In these experiments, the ionic strength was adjusted by addition of 3 M KCl in Hepes buffer. The concentration of 1-PB was 40 μM. Other conditions were as in Fig. 1.