Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV–vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate

Hydroxypyridinone and 5-Aminolaevulinic Acid Conjugates for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising treatment strategy for malignant and nonmalignant lesions. 5-Aminolaevulinic acid (ALA) is used as a precursor of the photosensitizer, protoporphyrin IX (PpIX), in dermatology and urology. However, the effectiveness of ALA-PDT is limited by the relatively poor bioavailability of ALA and rapid conversion of PpIX to haem. The main goal of this study was to prepare and investigate a library of single conjugates designed to coadminister the bioactive agents ALA and hydroxypyridinone (HPO) iron chelators. A significant increase in intracellular PpIX levels was observed in all cell lines tested when compared to the administration of ALA alone. The higher PpIX levels observed using the conjugates correlated well with the observed phototoxicity following exposure of cells to light. Passive diffusion appears to be the main mechanism for the majority of ALA-HPOs investigated. This study demonstrates that ALA-HPOs significantly enhance phototherapeutic metabolite formation and phototoxicity

Sustained and efficient porphyrin generation in vivo using dendrimer conjugates of 5-ALA for photodynamic therapy

The use of endogenous protoporphyrin IX (PpIX) after administration of 5-aminolaevulinic acid (ALA) has led to many applications in photodynamic therapy (PDT). However the efficacy of ALA-PDT is sub-optimal for thicker tumours and improved ALA delivery and therapeutic response are required. We have investigated the conjugation of ALA to a second-generation dxcendrimer for enhancing porphyrin synthesis in vitro and in vivo in a murine tumour model using systemic i.p. administration. In vitro, the dendrimer was more efficient than ALA for porphyrin synthesis at low concentrations in good correlation with higher cellular ALA dendrimer accumulation. In vivo, the porphyrin kinetics from ALA exhibited an early peak between 3 and 4 h in most tissues, whereas the dendrimer induced sustained porphyrin production for Over 24 h and basal values were not reached until 48 h after administration. Integrated porphyrin accumulation from the dendrimer and ALA, at equivalent molar ratios, was comparable showing that the majority of ALA residues were liberated from the dendrimer. The porphyrin kinetics appear to be governed by the rate of enzymatic cleavage of ALA from the dendrimer, which is consistent with in vitro results. ALA dendrimers may be useful for metronomic PDT, and Multiple low-dose ALA-PDT treatments