Cytochrome active species

Most likely the flavin triplet is the photochemically active species and the flavin semiquinone is the reducing agent for the b-type cytochrome. 

Ohe T, Mashino T, Hirobe M. Substituent elimination from p-substituted phenols by cytochrome P450. Ipso-substitution by the oxygen atom of the active species. Drug Metab Dispos 1997 25(1) 116-122. 

By analogy between the oxo forms of vanadium(V) and iron(IV), the latter being the active species in oxidations by cytochrome P-450, the system constituted by vanadium oxide as the catalyst, and t-butylhydro-peroxide, as the oxidant, gives good results in the conversion of olefins to the corresponding epoxides. With the supported "clayniac" catalyst, in the presence of i-butyraldehyde as a sacrificial reducer, olefins are epoxidized in good yields by compressed air at room temperature, in a convenient procedure. 

There is no valid interpretation for the activation by OJ and by hexacyano-ferrate(III), although they fitted nicely in a reaction scheme with Cu(III) as the active species In the oxidation of an alcohol to an aldehyde Cu(III) would be reduced to Cu(I). In the subsequent reaction of Cu(I) with Oj, Cu(II)Oj was considered an intermediate yielding Cu(III) and H O. This intermediate would be in a reversible equilibrium with OJ and with the resting Cu(II)-enzyme. This resting enzyme would be oxidized by hexacyanoferrate(III) to the active Cu(III) species. There was unfortunately no indication in X-ray absorption measurements for the formation of Cu(III) with hexacyanoferrate(III) and the resting enzyme . EPR measurements indicated that Cu(II) was present in the active enzyme It was not possible, moreover, to detect Oj by the reduction of Fe(III)-cytochrome c in a galactose oxidase — galactose system... 

Certain furan derivatives show selective organ toxicity in animals. One such chemical is 4-ipomeanol (54 see Table 8 for structures), which is toxic to specific cells (Clara cells) in the lungs of treated animals (77MI10501). Administration results in bronchiolar cell necrosis, extensive pulmonary oedema and subsequent death of the animal. Experiments have shown that ipomeanol is localized within the Clara cell (77MI10501), which is considered to be rich in cytochrome P450 (78MI10505), an important enzyme complex for metabolism. The ipomeanol is then converted via the cytochrome P450 into an activated species that alkylates... 

Several diverse metal centres are involved in the catalysis of monooxygenation or hydroxylation reactions. The most important of these is cytochrome P-450, a hemoprotein with a cysteine residue as an axial ligand. Tyrosinase involves a coupled binuclear copper site, while dopamine jS-hydroxylase is also a copper protein but probably involves four binuclear copper sites, which are different from the tyrosinase sites. Putidamonooxin involves an iron-sulfur protein and a non-heme iron. In all cases a peroxo complex appears to be the active species. 

The mechanism of the epoxidation of alkenes by the cytochrome P450 model, sodium hypochlorite-manganese(III) tetraarylporphyrins, involves rate-determining formation of an active species 234 from a hypochlorite-manganese complex 233 (Scheme 6) pyridine or imidazole derivatives, as axial ligands, accelerate this step by electron donation, although the imidazoles are destroyed under the reaction conditions368. 

Carbenes as Ligands. As mentioned above, TPPFe complexes have been reported to be active catalysts in carbon transfer reactions, in which the active species are assumed to be iron porphy-rin carbene complexes. " Since carbene complexes are typically synthesized as models of cytochrome P450 enzymes, they are discussed in the corresponding section on P450 models. Section 8.2. 

Shaik S, Hirao H, Kumar D. Reactivity patterns of cytochrome P450 enzymes multifunctionality of the active species, and the two states-two oxidants conundrum. Nat. Prod. Rep. 2007 24 533-552. 

The opportunity of obtaining direct electrochemistry of cytochrome c and other metalloproteins at various electrode materials such as modified gold and pyrolytic graphite has led to numerous reports of heterogeneous electron transfer rates and mechanisms between the protein and the electrode. In all the reports, Nicholson s method (37) was employed to calculate rate constants, which were typically within the range of 10" -10 cm sec with scan rates varying between 1 and 500 mV sec This method is based on a macroscopic model of the electrode surface that assumes that mass transport of redox-active species to and from the electrode occurs via linear diffusion to a planar disk electrode and that the entire surface is uniformly electroactive, i.e., the heterogeneous electron transfer reaction can take place at any area. 

---