Figure 10.

Approximation of the MCD spectrum of X obtained by subtracting the spectrum of IDS-oxidized ΔnifB NifDK (i.e., the P²⁺ spectrum, shown in Figure 6B) from the spectrum of OAR ΔnifH NifDK (i.e., the 6 T spectrum in Figure 4B). Both spectra were recorded at 1.6 K and 6 T. The intensity of the spectrum of ΔnifB NifDK used in the subtraction was reduced to ¹/₄ to approximate the concentration of the P²⁺ cluster in the composite spectrum.