CONICET | Buscador de Institutos y Recursos Humanos

MccJ25 is an antimicrobial peptide that targets both, the transcription process and the bacterial membrane respiratory chain, inhibiting cell oxygen consumption. This last effect is mediated by an increase in superoxide production by the respiratory processes. Tyr9 of MccJ25 was demonstrated as essential for the action on the respiratory chain. Redox-active tyrosine residues play important roles in catalysis in several enzymes, including ribonucleotide reductase, prostaglandin H synthase, and Photosystem II [1]. Here we investigated the tyrosil radical formation in MccJ25 using Electronic Paramagnetic Resonance (EPR) and Fourier transform infrared spectroscopy (2D-FTIR). The tyrosil radical was detected by EPR when MccJ25 was incubated in the presence of H2O2 and DBNBS (trapping of the tyrosil radical). Moreover, FTIR experiments showed an increment of tyrosil radical band located at 1,478 cm-1 in the spectrum. Moreover the redox potential of microcina J25 was determinated by cyclic voltammetry techniques and an irreversible oxidation at about 970 mV vs calomel electrode was detected, a value corresponding to tyrosine oxidation. On other hand, MccJ25 was unable to inhibited respiratory chain enzymes activities when the experiments were performed with membranes obtained from E. coli deficient in cytochrome bd and quinones production pathways. These results confirm the presence of a tyrosil radical in MccJ25 molecule and suggest that it could be formed by oxidation in the respiratory chain. Moreover, we proposed that cytochrome bd and quinores are essential for the MccJ25 effect on respiratory chain. [1] Vassiliev, I. R., Offenbacher, A. R., Barry, B. A.,J. Phys. Chem. B., 2005,109:23077-23085.