Adrenodoxin reductase and adrenodoxin. Mechanisms of reduction of ferricyanide and cytochrome c

J Biol Chem. 1977 May 10;252(9):2908-17.


Adrenodoxin reductase, the flavoprotein moiety of the adrenal cortex mitochondrial steroid hydroxylating system, participates in adrenodoxin-dependent cytochrome c and adrenodoxin-independent ferricyanide reduction, with NADPH as electron donor for both of these 1-electron reductions. For ferricyanide reduction, adrenodoxin reductase cycles between oxidized and 2-electron-reduced forms, reoxidation proceeding via the neutral flavin (FAD) semiquinone form (Fig. 9). Addition of adrenodoxin has no effect upon the kinetic parameters of flavoprotein-catalyzed ferricyanide reduction. For cytochrome c reduction, the adrenodoxin reductase-adrenodoxin 1:1 complex has been shown to be the catalytically active species (Lambeth, J. D., McCaslin, D. R., and Kamin, H. (1976) J. Biol. Chem. 251, 7545-7550). Present studies, using stopped flow techniques, have shown that the 2-electron-reduced form of the complex (produced by reaction with 1 eq of NADPH) reacts rapidly with 1 eq of cytochrome c (k approximately or equal to 4.6 s-1), but only slowly with a second cytochrome c (k = 0.1 to 0.3 s-1). However, when a second NADPH is included, two more equivalents of cytochrome are reduced rapidly. Thus, the adrenodoxin reductase-adrenodoxin complex appears to cycle between 1- and 3-electron reduced states, via an intermediate 2-electron-containing form produced by reoxidation by cytochrome (Fig. 10). For ferricyanide reduction by adrenodoxin reductase, the fully reduced and semiquinone forms of flavin each transfer 1 electron at oxidation-reduction potentials which differ by approximately 130 mV. However, adrenodoxin in a complex with adrenodoxin reductase allows electrons of constant potential to be delivered from flavin to cytochrome c via the iron sulfur center...

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenal Cortex / analysis
  • Adrenodoxin / metabolism*
  • Animals
  • Binding Sites
  • Binding, Competitive
  • Cattle
  • Cytochrome c Group / metabolism*
  • Electron Transport
  • Ferredoxin-NADP Reductase / antagonists & inhibitors
  • Ferredoxin-NADP Reductase / metabolism*
  • Ferricyanides / metabolism*
  • Kinetics
  • Mitochondria / analysis
  • Models, Biological
  • NADH, NADPH Oxidoreductases / metabolism*
  • NADP / metabolism
  • Oxidation-Reduction
  • Protein Binding
  • Thermodynamics


  • Cytochrome c Group
  • Ferricyanides
  • Adrenodoxin
  • NADP
  • Ferredoxin-NADP Reductase
  • NADH, NADPH Oxidoreductases