Adsorbed redox metalloprotein

The electrochemistry of metalloproteins has developed markedly (4-6) over the past 15 years. It has mainly been concerned with the electrochemistry at solid electrodes gold, upon which are adsorbed redox-inactive promoters, i.e., molecules that bind both to the electrode and the protein and edge-plane graphite, with or without redox-inert metal ions in solution. 

With a few exceptions, redox metalloprotein voltammetry on gold surfaces is unstable or absent unless either the electrode is modified by chemisorbed monolayers of linker or promoter molecules, or the protein is modified by insertion of non-native amino acid residues. The linker molecules are usually thiol-containing molecules which adsorb strongly on the Au-surface. 

Overall the single-crystal voltammetry, surface promoter sensitivity, and in situ STM of PJ d illuminate procedures and approaches to highly increased resolution in the bioelectrochemical mapping of redox metalloproteins, approaching the electrochemical resolution of small molecular adsorbate molecules. 

Sumi H (1998) V-I characteristics of STM processes as a probe detecting vibronic interactions at a redox state in large molecular adsorbates such as metalloproteins. J Phys Chem B 102 1833-1844... 

It has been shown that a variety of complex redox-linked properties of metalloproteins can be probed by voltammetry of these species adsorbed on the electrodes. Armstrong has been a key investigator in this area, and he has elegantly reviewed salient recent advances (33) the following paragraphs merely summarize some of the highlights of his review... 

Investigations of multicentre electrochemical metalloprotein function including metalloenzyme function have also been brought to a level, where both direct and catalytic modes, and elements of molecular mechanisms can be addressed. The latter are, however, entangled by features such as composite electrochemistry, extremely complicated molecular interaction patterns when more than two metallic redox centres are involved, fragile surface enzyme preparations, and lack of structural surface characterization of the adsorbed metalloenzymes. In this respect, two-centre metalloproteins constitute interesting promising intermediates where the coop-erativity between the metallic redox centres can be accurately addressed with molecular resolution within reach. 

Armstrong, F. A., Butt, J. N., and Sucheta, A., 1993, Voltammetric studies of redox-active centres in metalloproteins adsorbed on electrodes, Meth. Enzymol. 227 479n500. 

By contrast, the Hg electrode has not fared well in studies of electron-transfer metalloproteins. In almost all cases, the electrochemical response has been dominated by undesirable features signals arising from adsorbed molecules, which do not reflect the accepted redox chemistry of the metal centres, and irreversible waves due to sluggish reduction and reoxidation of protein molecules in bulk solution. Nevertheless, the studies that have been made are informative and some wilt be mentioned briefly here. All potentials given in this article have been corrected to correspond with the Standard Hydrogen Electrode (SHE). 

---