Spectroscopic and electrochemical studies of horse myoglobin in dimethyl sulfoxide

Abstract

This paper reports the first report of rapid, reversible direct electron transfer between a redox protein, specifically, horse myoglobin, and a solid electrode substrate in nonaqueous media and the spectroscopic (UV-vis, fluorescence, and resonance Raman) characterization of the relevant redox forms of myoglobin (Mb) in dimethyl sulfoxide (DMSO). In DMSO, the heme active site of metmyoglobin (metMb) appears to remain six-coordinate high-spin, binding water weakly. Changes in the UV-fluorescence spectra for metMb in DMSO indicate that the protein secondary structure has been perturbed and suggest that helix A has moved away from the heme. UV-vis and RR spectra for deoxyMb in DMSO suggest that the heme iron is six-coordinate low-spin, most likely coordinating DMSO. Addition of CO to deoxyMb in DMSO produces a single, photostable six-coordinate CO adduct. UV-vis and RR for Mb-CO in DMSO are consistent with a six-coordinate low-spin heme iron binding His93 weakly, if at all. The polarity of the distal heme pocket is comparable to that of the closed form of horse Mb-CO in aqueous solution, pH 7. Direct electron transfer between horse Mb and Au in DMSO solution was investigated by cyclic voltammetry. Mb exhibits stable and well-defined electrochemical responses that do not appear to be affected by the water content (1.3-7.5%). The electrochemical characteristics are consistent with a one-electron, quasi-reversible, diffusion-controlled charge transfer process at Au. E degrees for horse Mb in DMSO at Au is -0.241+/-0.005 V vs. NHE. The formal heterogeneous electron transfer rate constant, calculated from delta E(p) at 20 mV/s, is 1.7+/-0.5 x 10(-4) cm/s. The rate, which is unaffected by the presence of 1.3-7.5% water, is competitive with that previously reported for horse Mb in aqueous solution.

Electrochemical investigation of the effect of some organic phosphates on haemoglobin

“…Numerous efforts have been made to improve electron transfer characteristics by using mediators, promoters and direct electron transfer for haemoproteins (Eddowes and Hill 1977;Ye and Baldwin 1988;Dong et al 1989;Chen et al 1994;Lu et al 1994;Li et al 1999;Kuramitz et al 1999;Fan et al 2001). There are also reports of elucidation of structural information by electrochemical methods on haemoproteins such as cytochrome c, myoglobin and haemoglobin; these methods investigate the folding and unfolding of proteins, and the effects of ligand-binding and inorganic solvents on the structure of proteins (Funk et al 1990;Sarma et al 1997;Li and Mabrouk 2003;Peng et al 2003). Many studies on the structure of haemoglobin by electrochemical methods (Funk et al 1990;Faulkner et al 1994;Peng et al 2003;Zhang et al 2004;Sun et al 2004;Scheller et al 2005) have reported that electrochemical methods can be used to determine the structural changes that take place in the folding process of cytochrome c (Moosavi-Movahedi et al 2003), and electrochemical methods were applied to investigate the structural properties of haemoglobin in the presence of ligands, adenosine-5′-triphosphate (ATP) and other materials (Peng et al 2003).…”

Redox reactions and enzyme-like activities of immobilized myoglobin in aqueous/organic mixtures

“…The use of aqueous mixtures of organic co-solvents for conducting enzymatic reactions has become highly promising in biotechnology processes [22]. Recently many researchers have been devoted to investigating the electrochemical properties of redox proteins in organic solvents [23,24]. However, there are few reports on electrochemically catalytic properties of immobilized Mb in aqueous/organic mixtures [8].…”

An Effector of Hemoglobin Structure: The Guanosine 3', 5'-Triphosphate

“…While, the heme group would change its position from the inside to the surface of hemoglobin. [21][22][23] It seems that GTP can bind and change the secondary and tertiary structures of hemoglobin. We showed that reason of the decreased affinity of hemoglobin for oxygen, as stated by Tamburrini et al, 11 may be because of the changed secondary and tertiary structures of hemoglobin.…”