Low temperature electron paramagnetic resonance studies on iron-sulfur centers in cardiac NADH dehydrogenase

EPR signals arising from at least seven iron-sulfur centers were resolved in both reconstitutively active and inactive NADH dehydrogenases, as well as in particulate NADH-UQ reductase (Complex I). EPR lineshapes of individual iron-sulfur centers in the active dehydrogenase are almost unchanged from that in Complex I. Iron-sulfur centers in the inactive dehydrogenase give broadened EPR spectra, suggesting that modification of iron-sulfur active centers is associated with loss of the reconstitutive activity of the dehydrogenase. With the reconstitutively active dehydrogenase, the E_m8.0 value of Center N-2 (iron-sulfur centers associated with NADH dehydrogenase are designated with prefix N) was shifted to a more negative value than in Complex I and restored to the original value on reconstitution of the enzyme with purified phospholipids.