EFFECT OF POLYGLUTAMATE ON THE THERMAL-STABILITY OF FERRICYTOCHROME-C

The effect of saturated solutions of polyglutamate on the thermal stab ilities of the Met-80-heme iron bond and of the ferricytochrome c as a whole were studied by absorption spectroscopy and differential scanni ng calorimetry at pH 7.0. According to spectral data the midtransition temperature of the cleavage of the sulfur-iron bond was 57.4 +/- 0.5 degrees C and 66.8 +/- 0.5 degrees C for cytochrome c and cytochrome c -polyglutamate complex, respectively. Addition of polyglutamate to cyt ochrome c at pH 7.0 alters the denaturation properties of the protein. As follows from DSC scans, the denaturation temperature for cytochrom e c is decreased from 85.4 +/- 0.2 degrees C to 68.7 +/- 0.2 degrees C in the presence of the saturated amount of polyglutamate. The protein stability in terms of Gibbs energy change at protein unfolding amount to Delta G(25 degrees C) = 22.7 +/- 2.7 and 32.0 +/- 2.2 kJ/mol, for cytochrome c and cytochrome c-polyglutamate complex, respectively, at pH 7.0. It is evident that polyglutamate increases the thermal stabili ty of the sulfur-iron bond and decreases the denaturation temperature of the cytochrome c molecule as a whole. The complex thermal stability in terms of Gibbs energy is not lower than that of cytochrome c in th e range of physiological temperatures.