Cytochrome promoters

A more detailed study of the biological oxidation of sulphoxides to sulphones has been reported165. In this study cytochrome P-450 was obtained in a purified form from rabbit cells and was found to promote the oxidation of a series of sulphoxides to sulphones by NADPH and oxygen (equation 56). Kinetic measurements showed that the process proceeds by a one-electron transfer to the activated enzymatic intermediate [an oxenoid represented by (FeO)3+] according to equation (57). 

While it has been known for many years that the N-terminal presequence is sufficient to promote mitochondrial targeting and assembly, the subsequent interaction of the precursor molecule with the outer mitochondrial membrane and the uptake of the protein is still an area of active research. There seems little doubt, however, that there are proteins on the outer mitochondrial membrane which are required for the import process. The function of these proteins is uncertain, but they may act as receptors with the subsequent transfer through the membrane at proteinous pores located at contact sites between the inner and outer membranes. Several proteins have been identified which seem to play an important role as either receptor proteins or part of the import channel (Pfanner et al., 1991). Again, not all proteins seem to depend on this mechanism. Cytochrome c, which is loosely associated with the outer aspect of the inner mitochondrial membrane, can cross... 

Two main apoptotic pathways have been identified in mammalian cells the extrinsic pathway that is activated by the binding of ligands to cell-surface death receptors, and the intrinsic pathway that involves the mitochondrial release of cytochrome cP The activation of extrinsic and intrinsic apoptotic pathways promotes the cleavage into the active form of the pro-caspase-8 and pro-caspase-9, respectively, that mainly determine the activation of effector caspase-3. ° The intrinsic pathway is the main apoptotic pathway activated by chemotherapeutic drugs, while the cytotoxic drug-induced activation of the extrinsic pathway is a more controversial issue. ... 

Figure 12-8. Principles of the chemiosmotic theory of oxidative phosphorylation. The main proton circuit is created by the coupling of oxidation in the respiratory chain to proton translocation from the inside to the outside of the membrane, driven by the respiratory chain complexes I, III, and IV, each of which acts as a protonpump. Q, ubiquinone C, cytochrome c F Fq, protein subunits which utilize energy from the proton gradient to promote phosphorylation. Uncoupling agents such as dinitrophenol allow leakage of H" across the membrane, thus collapsing the electrochemical proton gradient. Oligomycin specifically blocks conduction of H" through Fq.

Li, L. Y., Amidon, G. L., Kim, J. S., Heimbach, T.j Kesisoglou, F. et al., Intestinal metabolism promotes regional differences in apical uptake of indinavir coupled effect of P-glycoprotein and cytochrome P450 3A on indinavir membrane permeability in rat, /. Pharmacol. Exp. Ther. 2002, 301, 586-593. 

In the original paper, Eddowes and Hill (1977) had reported that, in addition to 4,4 bipyridine, 1,2 bis(4-pyridyl) ethylene (2) was a more effective promoter of cytochrome c electrochemistry than the 4,4 bipyridine and SSBipy was better than both. This lead Allen and colleagues (1984) to postulate that the prerequirement for successful promoter activity was bifunctionality of the form ... 

The results clearly showed the importance of directionality. 4-lhiopyridine is an excellent promoter, while the 2 isomer shows no activity. After adsorption the 4 isomer has the pyridine nitrogen direction out into solution while the 2 isomer points the N back towards the electrode where it is available for adsorption to the gold rather than the cytochrome c. 

At this point it was clear how SSBipy was adsorbed on the electrode and the timescale over which this occurred, as well as the role of the concentration of the initial solution. However, the actual mode of action of the adsorbed species still remained somewhat obscure. An important insight into this was provided by the work of Hill et al. in 1987 who studied the effect of partial substitution of the layer of adsorbed promoter on the electrochemistry of cytochrome c. 

The first reports on direct electrochemistry of a redox active protein were published in 1977 by Hill [49] and Kuwana [50], They independently reported that cytochrome c (cyt c) exhibited virtually reversible electrochemistry on gold and tin doped indium oxide (ITO) electrodes as revealed by cyclic voltammetry, respectively. Unlike using specific promoters to realize direct electrochemistry of protein in the earlier studies, recently a novel approach that only employed specific modifications of the electrode surface without promoters was developed. From then on, achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters had made great accomplishments. 

The answer is b. (Katzungr pp 806—807J Rifampin induces cytochrome P450 enzymes, which causes a significant increase in elimination of drugs, such as oral contraceptives, anticoagulants, ketoconazole, cyclosporine, and chloramphenicol. It also promotes urinary excretion of methadone, which may precipitate withdrawal. 

The pioneering works of Hill and Eddows have opened the way to realize fast and efficient electron transfer of enzymes at the electrode surface. They modified a gold electrode with 4,4 -bipyrydyl, an electron promoter, not a mediator since it does not take part in electron transfer in the potential region of interest, to accomplish rapid electron transfer of cytochrome [1], Their work has triggered intensive investigation of electron transfer of enzymes using modified electrodes [2]. 

The above sequence mimics the proposed biosynthesis of Ervatamia alkaloids and in this context Thai and Mansuy (190) set out to determine whether an enzyme preparation would be able to promote the same transformation. By incubation of dregamine hydrochloride with a suspension of liver microsomes from a rat pretreated with phenobarbital (as a good inducer of P-450 cytochromes) in the presence of NADPH and 02, 20-epiervatamine (45) was formed together with the major metabolite Nl -demethyldregamine. It is well known that microsomal reaction on tertiary amines results in Af-oxide formation or N-deal-kylation. Thus it is likely that 45 was derived either from a rearrangement of dregamine JV4-oxide, catalyzed by the iron cytochrome P-450 or from one-electron oxidation of 30. 

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