| Abstract [eng] |
Electron Transfer in Multicenter Flavoenzymes Multicenter flavoenzymes that belong to dehydrogenases – electron transferases convert two-electron transfer into one-electron transfer and are important both in biosensorics and xeniobiotics metabolism. Two electrons are transferred from the substrate to reduce the flavin which reduces heme in two intramolecular one-electron transfers. These electrons are then transferred intermolecularly to the terminal electron acceptor. Two members of this class were studied using steady-state kinetics and electrochemistry, namely flavocytochrome b2 (fcb2) from yeast Saccharomyces cerevisiae and flavohemoglobin (fHb) from bacteria Staphylococcus aureus. The goal was to investigate the electron transfer during the reactions between said enzymes and nonphysiological electron acceptors quinones. It was shown that the reaction rate increases with increasing quinone redox potential in the case of fcb2. Based on our previous research on fcb2 and its properties we carried out electrochemical analysis to assess its proposed use in biosensorics. The electro-oxidation of L-lactate begins upon reaching the oxidation potential of the immobilized mediator with electron transfer constant equal to about 0,7 s-1 during these electrochemical changes of the mediators. Moreover, the KMapp was lower when compared to homogenous catalysis, but the half-life of these systems appeared to be quite short. It was found that the kinetics of fHb catalyzed reduction reaction exhibit a ping-pong mechanism. There is no clear dependence between quinone reactivity and increase in their redox potential, and this can be attributed to a mainly two-electron nature of this reaction. Azole inhibitors appear to activate the fHb reaction with quinones by lowering the KM for NADH and this implies the combination of said compounds in target drug design. |
