Fig. 4.

Time-dependent P-cluster formation on Av1^ΔnifZΔnifB. Shown are average activities (A), perpendicular-mode EPR spectra (B), parallel-mode EPR spectra (C), and visible-range absorption spectra (D) of Av1^{ΔnifZΔnifB(0)} (A, black bar; B–D, black lines), Av1^{ΔnifZΔnifB(15′)} (A, red bar; B–D, red lines), Av1^{ΔnifZΔnifB(30′)} (A, green bar; B–D, green lines), Av1^{ΔnifZΔnifB(45′)} (A, brown bar; B–D, brown lines), and Av1^{ΔnifZΔnifB(60′)} (A, blue bar; B–D, blue lines). EPR and visible-range absorption spectra were measured at protein concentrations of 10 and 5 mg/ml, respectively, as described in Materials and Methods. The time-dependent change of the visible-range absorption spectra during P-cluster maturation is indicated by the red arrow. The g values of the EPR spectra are indicated. The perpendicular (B) and parallel-mode EPR signals (C) are integrated as percentages of that of Av1^{ΔnifZΔnifB(0)} (set as 50%).^¶