FIGURE 2.

Reduction of the Fe/S clusters of complex I and the E183H^F variant by nucleotides. Complex I was reduced with a 1,000-fold molar excess of both NADH (trace a) and NADPH (trace b). The E183H^F variant was reduced with a 1,000-fold molar excess NADPH (trace c). The spectra in A were recorded at 40 K and 2 milliwatts of microwave power, and the spectra in B were recorded at 13 K and 5 milliwatts of microwave power. Other EPR conditions were as follows: microwave frequency, 9.44 GHz; modulation amplitude, 0.6 mT; time constant: 0.124 s; scan rate: 17.9 mT/min.