J. Biol. Chem., Vol. 259, Issue 11, 6931-6936, 06, 1984
Spectral studies of horse heart porphyrin cytochrome c
JM Strottmann, A Stellwagen, C Bryant and E Stellwagen
Removal of the heme iron from cytochrome c to generate porphyrin cytochrome
c relieves the quenching of porphyrin fluorescence and enhances the
fluorescence of the single tryptophan residue and the 4 tyrosine residues.
The intensity of the porphyrin fluorescence is not perturbed by
denaturation of the protein at neutral pH using either urea or guanidine
hydrochloride. However, the amplitude of tryptophan fluorescence is
increased by these denaturants from 5 to about 85% of a model tryptophan
residue using solutions of 2 microM tryptophan. In contrast to cytochrome
c, the tryptophan fluorescence amplitude of denatured porphyrin cytochrome
c is independent of pH over the range pH 3.0 to 7.4. Acidification of
solutions of either native or denatured porphyrin cytochrome c markedly
alters both the visible absorbance and fluorescence of the protein
consistent with protonation of two pyrrole nitrogens on the porphyrin.
Preliminary analysis of the spectral changes occurring in the acid
transition suggests the presence of an intermediate form having only one of
these two pyrrole nitrogens protonated.
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