Intramolecular oxidation of cytochrome c by covalently attached sulfoaromatic molecules

Two photosensitive molecules, 1-maleimidopyrene-3,6,8-trisulfonate (MPTS) and N-acetylaminoethyl-1-aminonaphthalens-5-sulfonate (AEDANS), are employed to drive the intramolecular oxidation of the heme residue in cytochrome c. intense pulse illumination (60-120 MW cm^-2) of MPTS and AEDANS in the aqueous solution by the third harmonic frequency of Nd-Yag laser drives a two successive-photon process of the dyes. The oxidized products originating from the dyes react with variety of electron donors. MPTS and AEDANS residues were covalently linked the Saccharomyces cerevisiae iso-1-cytochrome c by labeling of its single sulfhydryl group. When pulsed by intensive laser beam the heme of the labeled ferrocytochrome c undergoes fast oxidation. Transient absorption spectroscopy was used to directly measure the rate constants for the photoinduccd electron-transfer reaction from the ferros heme group to the oxidized dyes. The rate constant was found to be (3.6 ± 0.4) x 10⁴ s^-1 for MPTS derivative. The rate of the heme oxidation in AEDANS derivative was faster than response time of our detection system (20 ns). Rapid photooxidation of cytochrome c makes it a useful tool for Fast initiation of electron transfer in oxidized direction within complexes of cytochrome c with the other redox proteins.