INTERACTION OF FERRICYTOCHROME-C WITH POLYANION NAFION

The properties of the complex of ferricyt c with fluorosulfonated poly anion Nafion (as a representative 'hydrophobic' polyanion) have been s tudied by means of optical spectroscopy and differential scanning calo rimetry. The addition of the polyanion to a solution of fenicyt c (pH 7.4) resulted in an expansion of the protein molecule characterized by a profound decrease in enthalpy of the thermal transition of fenicyt c. The conformational change of ferricyt c upon addition of Nafion was shown by a perturbation of the Met-80-heme iron bond and an apparent increase in the distance of Trp-59 from the heme. The conformational c hange in the heme region was also observed by examining the CD spectra . The conformational state of fenicyt c in a complex with Nafion was s imilar to that designated as state II by Hildebrandt (Hildebrandt, P. (1990) Biochim. Biophys, Acta 1040, 175-186) in the complex with negat ively charged heteropolytungstates - a six-coordinated low-spin state with a destabilized structure of the heme crevice. The decrease in ent halpy of the thermal transition of ferricyt c, the spectral changes in absorbance and the CD spectra, together with an increase in Trp fluor escence induced by Nafion addition observed at high ionic strength, al l point to the involvement of the non-coulombic interaction. (C) 1997 Elsevier Science B.V.