Fig. 3.

EPR properties of NifB^Ma and NifB^Mt. (A) EPR spectra of dithionite-reduced (1) NifEN-B, (2) NifEN-B plus SAM, (3) NifB^Ma, (4) NifB^Ma plus SAM, (5) NifB^Mt, and (6) NifB^Mt plus SAM. Spectra were collected in perpendicular mode at 50 mW and 10 K. (B) Difference spectra between untreated and SAM-treated (1) NifEN-B, (2) NifB^Ma, and (3) NifB^Mt in the dithionite-reduced state. All difference spectra were derived from the corresponding spectra in A and multiplied by a factor of 1.5 for better visualization of features. (C) EPR spectra of IDS-oxidized (1) NifEN-B plus SAM, (2) NifEN-B, (3) NifB^Ma plus SAM, (4) NifB^Ma, (5) NifB^Mt plus SAM, and (6) NifB^Mt. The spectra of NifEN-B plus SAM (C, 1) and NifEN-B (C, 2) were multiplied by a factor of 0.5 for better adaptation to the size of the graph. The untreated NifEN-B contained some L clusters (C, 2) and, upon SAM treatment, more L clusters were generated in this protein (C, 1), as indicated by an increase in the magnitude of the L-cluster–specific, g = 1.94 signal. Spectra were collected in perpendicular mode at 50 mW and 15 K. (D) Difference spectra between untreated and SAM-treated (1) NifEN-B, (2) NifB^Ma, and (3) NifB^Mt in the IDS-oxidized state. All difference spectra were derived from the corresponding spectra in C, and the difference spectrum of NifEN-B (D, 1) was multiplied by a factor of 2. The g values are indicated.