Two synthetic genes coding for human and Arabidopsis cytochrome c, respectively, have been designed and constructed, and the recombinant proteins have been over-expressed in Escherichia coli cells. Thus a comparative analysis of the two heme proteins, including horse cytochrome c as a reference, has been performed. In addition to their physico-chemical properties, the redox behavior of the three proteins has been analyzed by following the kinetics of both their reduction by flavin semiquinones (lumiflavin, riboflavin, and FMN) and oxidation by cytochrome e oxidase. The resulting data indicate that the accessibility and electrostatic charge of the active site do not differ in a significant way among the three proteins, but human cytochrome e exhibits some intriguing differences when interacting with cytochrome c oxidase that could be related to the amino acid changes underwent by the latter along evolution. (c) 2006 Elsevier Inc. All rights reserved.