Putidaredoxin mechanism

These spectra, taken at variable temperatures and a small polarizing applied magnetic field, show a temperature-dependent transition for spinach ferredoxin. As the temperature is lowered, the effects of an internal magnetic field on the Mossbauer spectra become more distinct until they result at around 30 °K, in a spectrum which is characteristic of the low temperature data of the plant-type ferredoxins (Fig. 11). We attribute this transition in the spectra to spin-lattice relaxation effects. This conclusion is preferred over a spin-spin mechanism as the transition was identical for both the lyophilized and 10 mM aqueous solution samples. Thus, the variable temperature data for reduced spinach ferredoxin indicate that the electron-spin relaxation time is around 10-7 seconds at 50 °K. The temperature at which this transition in the Mossbauer spectra is half-complete is estimated to be the following spinach ferredoxin, 50 K parsley ferredoxin, 60 °K adrenodoxin, putidaredoxin, Clostridium. and Axotobacter iron-sulfur proteins, 100 °K. 

The first electron can be transferred to Fefs) by various chemical agents (methylviologen, dithionite), but a second electron can be transferred only to Fe<< —02 via putidaredoxin. In this reaction the putidaredoxin is both a reducing agent and an effector, but the mechanism is not yet well known. 

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... 

Tosha T, Yoshioka S, Hori H, Takahashi S, Ishimori K, Morishima I (2002) Molecular mechanism of the electron transfer reaction in cytochrome P450cam-putidaredoxin roles of glutamine 360 at the heme proximal site. Biochemistry 41 13883-13893... 

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