C-type cytochromes are classified into two main groups: i) cytochromes
which give fast electrochemical responses at the conventional electro
des in the absence of any promoter leg multi-heme cytochromes c(3)); i
i) cytochromes which need the presence of promoters or the use of modi
fied electrodes to exhibit fast electrochemical responses leg one-heme
mitochondrial cytochrome c). In the latter case, careful design of el
ectrode surface and composition of the solution are required for the a
ttainment of rapid and reversible electron-exchange reactions. Some ge
neral considerations are given on the 'electrochemical model'. In part
icular, binding interactions between the electrode and the protein can
take place in a similar manner to that occurring between physiologica
l partner proteins. Electrochemistry when coupled to other physical te
chniques can give more complete insights in the relationship between t
he redox properties, structure and function of c-type cytochromes. In
particular, in the case of polyheme cytochromes, promising results are
expected from the study of site-directed mutagenesis-modified cytochr
ome c(3).