Anaerobic chlorophyll isocyclic ring formation in Rhodobacter capsulatus requires a cobalamin cofactor. (57/1552)

The isocyclic ring of bacteriochlorophyll (BChl) is formed by the conversion of Mg-protoporphyrin monomethyl ester (MPE) to protochlorophyllide (PChlide). Similarities revealed by blast searches with the putative anaerobic MPE-cyclase BchE suggested to us that this protein also uses a cobalamin cofactor. We found that vitamin B(12) (B(12))-requiring mutants of the bluE and bluB genes of Rhodobacter capsulatus, grown without B(12), accumulated Mg-porphyrins. Laser desorption/ionization time-of-flight (LDI-TOF) MS and NMR spectroscopy identified them as MPE and its 3-vinyl-8-ethyl (mvMPE) derivative. An in vivo assay was devised for the cyclase converting MPE to PChlide. Cyclase activity in the B(12)-dependent mutants required B(12) but not protein synthesis. The following reaction mechanism is proposed for this MPE-cyclase reaction. Adenosylcobalamin forms the adenosyl radical, which leads to withdrawal of a hydrogen atom and formation of the benzylic-type 13(1)-radical of MPE. Withdrawal of an electron gives the 13(1)-cation of MPE. Hydroxyl ion attack on the cation gives 13(1)-hydroxy-MPE. Withdrawal of three hydrogen atoms leads successively to 13(1)-keto-MPE, its 13(2)-radical, and cyclization to PChlide.  (+info)

Porphyrin analogues as novel antagonists of fibroblast growth factor and vascular endothelial growth factor receptor binding that inhibit endothelial cell proliferation, tumor progression, and metastasis. (58/1552)

Fibroblast growth factors (FGFs) and vascular endothelial growth factor (VEGF) play a pivotal role in the multistep pathway of tumor progression, metastasis, and angiogenesis. We have identified a porphyrin analogue, 5,10,15,20-tetrakis(methyl-4-pyridyl)-21H,23H-porphine-tetra -p-tosylate salt (TMPP), as a potent inhibitor of FGF2 and VEGF receptor binding and activation. TMPP demonstrated potent inhibition of binding of soluble FGF receptor 1 (FGFR1) to FGF2 immobilized on heparin at submicromolar concentrations. TMPP inhibits binding of radiolabeled FGF2 to FGFR in a cell-free system as well as to cells genetically engineered to express FGFR1. Furthermore, TMPP also inhibits the binding of VEGF to its tyrosine kinase receptor in a dose-dependent manner. In an in vitro angiogenic assay measuring the extent of endothelial cell growth, tube formation, and sprouting, TMPP dramatically reduced the extent of the FGF2-induced endothelial cell outgrowth and differentiation. In a Lewis lung carcinoma model, mice receiving TMPP showed a marked inhibition of both primary tumor progression and lung metastases development, with nearly total inhibition of the metastatic phenotype upon alternate daily injections of TMPP at 25 microg/g of body mass. Finally, novel meso-pyridylium-substituted, nonsymmetric porphyrins, as well as a novel corrole-based derivative, with >50-fold increase in activity in vitro, had a significantly improved efficacy in blocking tumor progression and metastasis in vivo.  (+info)

Aggregation kinetics of extended porphyrin and cyanine dye assemblies. (59/1552)

The kinetics of J-aggregate formation has been studied for two chromophores, tetrakis-4-sulfonatophenylporphine in an acid medium and pseudoisocyanine on a polyvinylsulfonate template. The assembly processes differ both in their sensitivity to initiation protocols and in the reaction profiles they produce. The porphyrin's assembly kinetics, for example, displays an induction period unlike that of the cyanine dye. Two kinetic models are presented. For the porphyrin, an autocatalytic pathway in which the formation of an aggregation nucleus is rate-determining appears to be applicable; for the pseudoisocyanine dye, an equation derived for diffusion-limited aggregation of a fractal object satisfactorily fits the data. These models are shown to be useful for the analysis of kinetic data obtained for several biologically important aggregation processes.  (+info)

Theodore Woodward Award. Pathogenesis of biochemical abnormalities in protoporphyria. (60/1552)

In summary, FC gene mutations in patients with protoporphyric liver disease typically cause major structural alterations in the FC protein. However, the gene mutations by themselves do not satisfactorily account for the severe phenotype, as the same mutations are found in asymptomatic family members, and similar mutations are found in patients who do not develop liver disease. Thus there may be unidentified factors in the FC gene locus, or factors outside the locus, which are also important in determining the degree of protoporphyrin accumulation that occurs in an individual patient, hence, the potential for developing significant liver disease. Further studies are needed to clarify this possibility and identify those factors.  (+info)

The bystander effect in photodynamic inactivation of cells. (61/1552)

Treatment of MDCK II cells with the lipophilic photosensitizer tetra(3-hydroxyphenyl)porphyrin and light was found to induce a rapid apoptotic response in a large fraction of the cells. Furthermore, the distribution of apoptotic cells in microcolonies of eight cells was found to be different from the binomial distribution, indicating that the cells are not inactivated independently, but that a bystander effect is involved in cell killing by photodynamic treatment. The observation of a bystander effect disagrees with the common view that cells are inactivated only by direct damage and indicates that communication between cells in a colony plays a role in photosensitized induction of apoptosis. The degree of bystander effect was higher for cells dying by necrosis than for cell dying by apoptosis.  (+info)

Release of gelonin from endosomes and lysosomes to cytosol by photochemical internalization. (62/1552)

Gelonin, a type I ribosome-inactivating plant toxin, executes N-glycosidase activity on eukaryotic ribosomes. However, on intact cells, gelonin is relatively non-toxic, due to an incapability to penetrate cell membranes. Recently, a novel method, photochemical internalization (PCI), was invented for the translocation of membrane-impermeable molecules including gelonin to the cytosol [K. Berg et al., Cancer Res. 59 (1999) 1180-1183]. The combination of gelonin and photoactivation of endosomal and lysosomal localizing photosensitizers gives strong synergistic cytotoxic effects. In this study, we have evaluated the intracellular transport and stability of gelonin. By fluorescence microscopy, it was shown that gelonin co-localizes with the endosomal and lysosomal localizing photosensitizer, aluminum phthalocyanine with two sulfonate groups on adjacent phenyl rings, and both molecules re-localized to cytosol subsequently to light exposure. Gelonin accumulated in endosomal compartments by incubation at 18 degrees C was released to cytosol by PCI with concomitant inhibition of protein synthesis indicating that PCI can be executed through rupture of endosomal vesicles. The cathepsin inhibitor L-trans-epoxysuccinyl-leucyl amido(4-guanido)butane increased the cytotoxic effect of gelonin after PCI when gelonin was provided as a 2 h pulse followed by 4 h chase before PCI. Thus, although gelonin can enter the cytosol from lysosomes, lysosomal degradation is a limiting factor for the outcome of PCI of gelonin.  (+info)

Peroxynitrite is a major contributor to cytokine-induced myocardial contractile failure. (63/1552)

Proinflammatory cytokines depress myocardial contractile function by enhancing the expression of inducible NO synthase (iNOS), yet the mechanism of iNOS-mediated myocardial injury is not clear. As the reaction of NO with superoxide to form peroxynitrite markedly enhances the toxicity of NO, we hypothesized that peroxynitrite itself is responsible for cytokine-induced cardiac depression. Isolated working rat hearts were perfused for 120 minutes with buffer containing interleukin-1 beta, interferon-gamma, and tumor necrosis factor-alpha. Cardiac mechanical function and myocardial iNOS, xanthine oxidoreductase (XOR), and NAD(P)H oxidase activities (sources of superoxide) were measured during the perfusion. Cytokines induced a marked decline in myocardial contractile function accompanied by enhanced activity of myocardial XOR, NADH oxidase, and iNOS. Cardiac NO content, myocardial superoxide production, and perfusate nitrotyrosine and dityrosine levels, markers of peroxynitrite, were increased in cytokine-treated hearts. The peroxynitrite decomposition catalyst FeTPPS (5,10,15, 20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron[III]), the NO synthase inhibitor N(G)-nitro-L-arginine, and the superoxide scavenger tiron each inhibited the decline in myocardial function and decreased perfusate nitrotyrosine levels. Proinflammatory cytokines stimulate the concerted enhancement in superoxide and NO-generating activities in the heart, thereby enhancing peroxynitrite generation, which causes myocardial contractile failure.  (+info)

Thin molecular films of supramolecular porphyrins. (64/1552)

A relevant series of symmetric supramolecular porphyrins has been obtained by attaching four [RuII(bipy)2Cl] groups to the pyridyl substituents of meso-tetra(4-pyridyl)porphyrin and its metallated derivatives. These compounds display a rich electrochemistry and versatile catalytic, electrocatalytic and photochemical properties, associated with the ruthenium-bipyridine and the porphyrin complexes. These properties can be transferred to the electrodes by attaching thin molecular films of the compounds, by dip-coating, electrostatic assembly or electropolymerization. In this way, the interesting properties of those supermolecules and supramolecular assemblies can be used to prepare molecular devices and sensors.  (+info)