Cytochrome c₅₅₃ from Desulfovibrio vulgaris (Hildenborough)

Abstract

An electrochemical study of the periplasmic cytochrome c553 of Desulfovibrio vulgaris (Hildenborough) is presented. The dependence of the midpoint potential on temperature and pH was studied with cyclic voltammetry. The voltammograms obtained were reversible and revealed that this cytochrome showed fast electron transfer on a bare glassy carbon electrode. The midpoint potential at pH 7.0 and 25°C was found to be 62 mV versus the normal hydrogen electrode. It was observed that the temperature dependence was discontinuous with a transition temperature at 32°C. The standard reaction entropy at the growth temperature of the organism (37°C) was calculated to be AS"'= -234 J mol-' K-I. The pH dependence of the midpoint potential could be described with one pK of the oxidized form with a value of 10.6. The second-order rate constant for electron transfer between cytochrome css3 and the Fe-hydrogenase from D. vulgaris (H) was also determined with cyclic voltammetry. The equivalent rate constant for cytochrome c3 and hydrogenase was measured for comparison. The second-order rate constants are 2X 1O'M-I s-' for cytochrome c5s3 and 2X 10' M-' s-' for cytochrome c3. The kinetic parameters of the hydrogenase for both cytochromes were determined using the spectrophotometric hydrogen consumption assay. With cytochrome css3 this resulted in a K, of 46 pM and a maximum turnover number of 7

Structural Model of the Fe-Hydrogenase/Cytochromec 553 Complex Combining Transverse Relaxation-optimized Spectroscopy Experiments and Soft Docking Calculations

“…The relative high exposure of the heme to the solvent is the structural parameter modulating the low oxidoreduction potential of this cytochrome (20 mV) (8). Kinetic experiments (6) have shown that cytochrome c 553 has a rather high affinity for hydrogenase (K m 46 M) and that the electron transfer rate constant (k cat 710 s Ϫ1 ) is comparable to those generally reported in bimolecular electron transfer complexes.…”

“…Both enzymes are periplasmic and use c-type cytochromes as electron transfer partners (6). One of the oxidoreduction partners of Fe-hydrogenase is the periplasmic low potential cytochrome c 553 .…”

Equilibrium unfolding of a small low‐potential cytochrome, cytochrome c553 from Desulfovibrio vulgaris

“…was purified as described previously~Fauque et al, 1979;Yagi, 1979;Verhagen et al, 1994 Spectra were measured on a Hewlett-Packard 8452 diode-array spectrophotometer~absorption, 1 cm cell! and a Jasco-600 spectropolarimeter~CD, 1 mm cell for far-UV region, 1 cm cell for visible region!, at 20 8C.…”

Electrochemical study of the redox properties of [2Fe‐2S] ferredoxins Evidence for superreduction of the Rieske [2Fe‐2S] cluster

“…Not only is it possible to study redox potentials and their dependence on parameters like temperature and pH, but also kinetic data in the form of rate constants can be obtained [1]. An important advantage of the use electrochemistry is the possibility to extend the potential window beyond the values which can be obtained in solution with chemical reductants or oxidants.…”