Thermodynamics Research Today is a free monthly online journal that collates and summarizes the latest research about Thermodynamics, including details on enthalpy, entropy, energy transitions.

Redox thermodynamics of the ferric-ferrous couple of wild-type synechocystis KatG and KatG(Y249F).

Bellei M, Jakopitsch C, Battistuzzi G, Sola M, Obinger C

Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.

Crystal structures and mass spectrometric analyses of catalase-peroxidases (KatGs) from different organisms revealed the existence of a peculiar distal Met-Tyr-Trp cross-link. The adduct appears to be important for the catalase but not the peroxidase activity of bifunctional KatG. To examine the effect of the adduct on enzyme redox properties and functions, we have determined the thermodynamics of ferric reduction for wild-type KatG and KatG(Y249F), whose tyrosine-to-phenylalanine mutation prevents cross-link formation. At 25 degrees C and pH 7.0, the reduction potential of wild-type KatG is found to be -226 +/- 10 mV, remarkably lower than the published literature values. The reduction potential of KatG(Y249F) is very similar (-222 +/- 10 mV), but variable temperature experiments revealed compensatory differences in reduction enthalpies and entropies. In both proteins, the oxidized state is enthalpically stabilized over the reduced state, but entropy is lost on reduction, which is in strong contrast to horseradish peroxidase, which also features a much more pronounced enthalpic stabilization of the ferriheme. With both proteins, the midpoint potential increased linearly with decreasing pH. We discuss whether the observed redox thermodynamics reflects the differences in structure and function between bifunctional KatG and monofunctional peroxidases.

Published 11 April 2006 in Biochemistry, 45(15): 4768-74.
Full-text of this article is available online (may require subscription).

© 2005-2008 Thermodynamics Research Today. All Rights Reserved.