Fluorescence energy transfer studies of the interaction between adrenodoxin and cytochrome c.

نویسندگان

  • L M Geren
  • F Millett
چکیده

The interaction between beef adrenodoxin and horse heart cytochrome c was studied by measuring the fluorescence emission of the single tyrosine at residue 82 of adrenodoxin. Addition of cytochrome c at low ionic strength (5 n m sodium morpholinosulfonate, pH 7.5) decreased the 331 nm fluorescence consistent with the formation of a 1:l adrenodoxin-cytochrome c complex with a dissociation constant of 0.034 p ~ , and an energy transfer efficiency of 69%. The dissociation constant of the complex increased rapidly as the ionic strength was increased, demonstrating that electrostatic interactions were important to formation of the complex. Specific modification of lysines surrounding the heme crevice of cytochrome c also increased the dissociation constant of the complex, indicating that the binding site for adrenodoxin is located at the heme crevice of cytochrome c. The distance between adrenodoxin tyrosine 82 and the cytochrome c heme was estimated to be 17 to 34 A, assuming that the main cause of fluorescence quenching was Forster energy transfer to the heme. The major source of uncertainty in this calculation was the orientation factor. By taking into account the position of the heme relative to the binding surface of cytochrome c, we estimated that tyrosine 82 is about 8 to 25 A away from the cytochrome c binding site on the surface of adrenodoxin. The location of tyrosine 82 in the primary sequence of adrenodoxin shows that it could be well removed from the iron-sulfur center, which is presumably close to the binding site for cytochrome c.

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عنوان ژورنال:
  • The Journal of biological chemistry

دوره 256 20  شماره 

صفحات  -

تاریخ انتشار 1981