Mesopone cytochrome c peroxidase: functional model of heme oxygenated oxidases

Composite films of lecithin and heme proteins with electrochemical and electrocatalytic activities

Functional composite films made from lecithin micelles and the two heme proteins of met-myoglobin (Mb) and met-hemoglobin (Hb) are reported in this paper. Proteins in functional composite films have much higher rates of electron transfer than proteins in solutions on carbon paste (CP) electrodes. Cyclic voltammograms (CVs) all give a pair of well-defined and quasi-reversible peaks, corresponding to the heme FeIII/FeII redox couple of proteins. Differential pulse voltammograms (DPVs) also show the same formal potential (E0') values of proteins under identical conditions. Electronic and vibrational spectra indicate that proteins in these films are not denatured, but their conformational differences from native states may exist. The E0' value for Mb in the lecithin film is found to be pH dependent. The Mb lecithin film can catalytically reduce O2 and H2O2, and its analytical application to H2O2 determination is established.

Direct electrochemistry and Raman spectroscopy of sol-gel-encapsulated myoglobin

The direct electrochemistry of myoglobin (Mb) has been observed at a glassy carbon (GC) electrode coated with silica sol-gel-encapsulated Mb film. A well-behaved cyclic voltammogram is observed with a midpoint potential (E(1/2)) of -0.25 V vs Ag/AgCl in a pH 7.0 phosphate buffer. This potential, which is pH-dependent, is 70-90 mV more negative than the formal potential values obtained by using the spectroeletrochemical titration method at the same pH. Square wave voltametry (SWV) also shows a peak potential of -0.25 V for the reduction of Mb under the same experimental conditions. Both cathodic and anodic peak currents have a linear relationship with the scan rate. The midpoint potential decreases with pH, having a slope of -30 mV/pH. UV-vis and resonance Raman spectroscopic studies reveal that the sol-gel provides a bio-compatible environment where Mb retains a structure similar to its solution form, a 6-coordinated aquomet myoglobin. These results suggest that the silica sol-gel is a useful matrix for studying direct electrochemistry of other heme proteins.

The 1.13-A structure of iron-free cytochrome c peroxidase

The iron-free cytochrome c peroxidase (CCP) crystal structure has been determined to 1.13 A and compared with the 1.2-A ferric-CCP structure. Quite unexpectedly, removal of the iron has no effect on porphyrin geometry and distortion, indicating that protein-porphyrin interactions and not iron coordination or formation of the axial His-Fe bond determines porphyrin conformation. However, there are changes in solvent structure in the distal pocket, which lead to changes in the distal His52 acid-base catalyst. The observed ability of His52 to move in response to small changes in solvent structure is very likely important for its role as a catalyst in assisting in the heterolytic fission of the peroxide O-O bond.