title: Porphyrin fluorescence dominates UV photoemission of folded cytochrome c.
abstract: In this article we reinvestigate the bimodal fluorescence of cytochrome c (Cyt c) by using excitation-wavelength-dependent fluorescence spectroscopy. We show that its major contributions at pH 3-7 do not arise from tryptophan (Trp-59) fluorescence as hitherto assumed. Instead, different chromophores of Cyt c contribute at different pH values. At pH 3-7, the porphyrin system contributes about 80% and tryptophan about 20% to the total fluorescence upon excitation of Cyt c at 280 nm. At pH 2, the fluorescence originates nearly completely from the tryptophan residue. Porphyrin fluorescence is still present at pH 2 but its contribution is too small for quantitative deconvolution. Our results show that the UV fluorescence of Cyt c has to be deconvoluted before it can be used to perform time-resolved measurements of the folding of this small protein.
authors.affiliation: Institute for Physical Chemistry, Heinrich-Heine-Universität, Düsseldorf, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Löwenich
authors.forename: Karl
authors.initials: K
authors.lastname: Kleinermanns
mesh_terms: D000818:Animals; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D006736:Horses / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry*; D017510:Protein Folding; D013050:Spectrometry, Fluorescence
chemical_list: D011166:Porphyrins; D045304:Cytochromes c