Influence of copper on the interaction between cytochrome c and sulfite in vitro.

The quantitative influence of copper on the interaction between cytochrome c and sulfite, which is a derivate of sulfur dioxide in the human body, has been studied by fluorescence spectrometry and ultraviolet absorption spectrometry in vitro. The results indicate that copper may intensely combine with protein component and ferroporphyrin component in cytochrome c at the concentration of 0.1 mM, and the respective association constants (K(A)) are 3.77 x 10(4) L mol(-1) and 9.38 x 10(3) L mol(-1). Sulfite has little interaction with the protein component in cytochrome c (K(A) = 0.094 L mol(-1)), at either low concentrations or relatively high concentrations (<0.15 M). However, it can react with the ferroporphyrin component in cytochrome c (K(A) = 4.297 L mol(-1)). After copper is added to the sulfite-cytochrome c binary systems, the reaction between sulfite and the protein component in cytochrome c is obviously strengthened at a low concentration (K(A) = 7.289 L mol(-1)), while the addition of copper merely has a little effect on the interaction between sulfite and the ferroporphyrin component in cytochrome c.