Sulfur Electron Donors Adrenodoxin, Putidaredoxin, and their Reductases

Iron-Sulfur Electron Donors Adrenodoxin, Putidaredoxin, and their Reductases 

The FcjS -type ferredoxins can be arranged into three distantly related classes based on amino acid sequence homologies bacterial-, plant-, and vertebrate-type . Extensive information on the function and mechanisms of this system has been gained through work on the bacterial P450cam system in Pseudomonas putida, which catalyzes the conversion of rf-camphor to 5-exo-hydroxy-camphor. In P putida, the iron-sulfur protein is putidaredoxin (Pdx), a 106 amino acid residue ferredoxin. For catalysis, two reducing equivalents are sequentially transferred from NADH 

In plants, [2Fe-2S] ferredoxins are involved in conjunction with ferredoxin-reductase in photosynthesis reactions and the transfer of electrons from photosystem I to NADP . However, evidence for involvement of ferredoxins in electron transfer to plant P450s awaits a more detailed characterization of the multiple P450 systems present in the biotechnologically important plant species. 

Ferredoxins receive their electrons from ferredoxin reductase, which represents the first component of the electron transfer system. These enzymes contain FAD and belong to a large group 

The rate-limiting steps in the entire catalytic cycle of P450cam are the electron transfers between Pdx and the P450. The precise rate-limiting step appears to change from the first electron transfer to the second electron transfer as the concentration of Pdx in the system is reduced toward levels considered typical of the situation in vivo.  

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