The combination of SPR biosensor with electrochemical analysis was used for the study of protein-protein interaction between cytochromes CYP3A4 or 3A5 and cytochromes b(5): the microsomal, mitochondrial forms of this protein, and 2 << chimeric >> proteins. Kinetic constants of CYP3A4 and CYP3A5 complex formation with cytochromes b(5) were determined by the SPR biosensor. Essential distinction between CYP3A4 and CYP3A5 was observed upon their interactions with mitochondrial cytochrome b(5). The electrochemical analysis of CYP3A4, CYP3A5, and cytochromes b(5) immobilized on screen printed graphite electrodes modified with membranous matrix revealed that these proteins have very close reduction potentials -0.435 to -0.350 V (vs. Ag/AgCl). (C) 2013 Elsevier B. V. All rights reserved.