Pseudoperoxidase activity and ascorbic acid oxidation of the cytochrome c fragment of Rhodotermus marinus caa3 oxygen reductase

LEANDRO BENAVIDES; MARÍA FLORENCIA MOLINAS; MARIA ANA CASTRO; DANIEL H. MURGIDA

Chascomús

Congreso; IV Latin American Meeting on Biological Inorganic; 2014

C-type cytochromes are not only soluble electron shuttles but are also often part of larger redox enzymes. Moreover, hemec containing protein domains can also be found fused to other domains. This is the case of the caa3 terminal oxygen reductase of Rhodothermus marinus, a Gram-negative strict aerobe thermophile bacterium. As in the mammalian counterparts, the catalytic site of the R. marinus enzyme is constituted by a binuclear hemea3 ? CuB center located in the subunit I. The main difference refers to subunit II which, in addition to the canonical CuA site, contains a cytochrome c domain (Cyt-D) in the C-terminal region that has been suggested as the primary acceptor of electrons transported by the putative donor, a periplasmic high-potential iron-sulfur protein (HiPIP). Cyt-D has been over-expressed in E. coli, yielding a well folded and stable soluble protein that retains the spectroscopic and redox properties of the domain in the holoenzyme1,2. It has been shown within our group that Cyt-D presents an increased general stability that suggests a possible use as a biosensor3. The replacement of highly sensitive redox enzymes with small electron transfer proteins in biolectronic devices provides several advantages such as: easier immobilization, easier electronic communication, increased stability and reusability4,5. Therefore, the Cyt-D mediated reduction of hydrogen peroxide (pseudoperoxidase activity)6 and oxidation of ascorbic acid are explored by cyclic voltammetry and chronoamperometry.