(1/1552) Do charge-remote fragmentations occur under matrix-assisted laser desorption ionization post-source decompositions and matrix-assisted laser desorption ionization collisionally activated decompositions?
The precursor ions of tetraphenylporphyrins that are substituted with fatty acids can be introduced into the gas phase by matrix-assisted laser desorption ionization (MALDI) and undergo post-source and collisionally activated decompositions (CAD) in a time-of-flight mass spectrometer. The goal of the research is to obtain a better understanding of post-source decompositions (PSD); specifically, we asked the question of whether ions undergoing PSD have sufficient energy to give charge-remote fragmentations along an alkyl chain. We chose the porphyrin macrocycle because we expected it to act as an inert "support," allowing the molecule to be desorbed by MALDI and to be amenable to charge-remote fragmentation. MALDI-PSD and MALDI-CAD spectra are similar to high-energy CAD spectra and considerably more informative than low-energy CAD spectra, showing that charge-remote fragmentations of the fatty acid moieties do occur upon MALDI-PSD and MALDI-CAD. (+info)
(2/1552) High efficiency of benzoporphyrin derivative in the photodynamic therapy of pigmented malignant melanoma.
Benzoporphyrin derivative monoacid ring A (verteporfin, BPD-MA) when intravenously injected (5.5 micromol kg(-1)) to C57/BL6 mice bearing a subcutaneously transplanted B1 melanoma gave a maximal accumulation in the tumour within 1-3 h with recoveries of 1.84-1.96 micromol kg(-1). Irradiation of BPD-MA-loaded melanoma with 690-nm light from a dye laser at 3 h and 9 h post injection induced tumour necrosis and delay of tumour growth of 28 and 14 days respectively. The response of the tumour to BPD-MA photosensitization was enhanced by pretreatment with 1064-nm light from a pulse-operated Nd:YAG laser, which caused a selective breakdown of melanosomes. (+info)
(3/1552) Ultrastructural changes in PAM cells after photodynamic treatment with delta-aminolevulinic acid-induced porphyrins or photosan.
Photodynamic therapy (PDT) is the combination of a photosensitizing drug (Ps) with light in the presence of oxygen leading to the generation of reactive molecular species and destruction of cancer cells. In this study we compared PDT with two Ps, the hematoporphyrin derivative Photosan (Ph) and delta-aminolevulinic acid (ALA)-induced endogenous protoporphyrin IX, with respect to mitochondrial function and ultrastructural alterations. The effects of PDT were investigated in PAM 212 cells after different Ps incubation times, light doses, and post-treatment periods. Both Ps induced a light dose-dependent impairment of the mitochondrial function with the dose-response curve being steep for ALA and flat for Ph. The prolongation of the incubation time from 4 to 20 h resulted in an increased reduction of mitochondrial activity after ALA PDT but not after Ph PDT. Treatment with an irradiation dose that decreased mitochondrial activity by 50% (IC50) led to early and profound changes of mitochondrial morphology in ALA photosensitized cells, whereas photosensitization with Ph resulted in more pronounced alterations of lysosomes. We conclude that at bioequivalent sublethal PDT exposures of PAM 212 cells, ALA-induced damage is primarily restricted to mitochondria, whereas Ph-induced cytotoxicity is mediated by damage of the lysosomal system. (+info)
(4/1552) Five-coordinate iron-porphyrin as a model for the active site of hemoproteins. Characterization and coordination properties.
Preparation of iron(III)-deuteroporphyrin 6(7)-methyl ester, 7(6)-(histidine methyl ester) by coupling histidine methyl ester to deuterohemin has been performed using the mixed carboxylic/carbonic-acid-anhydride method. This compound, which is very soluble in various organic solvents, can be considered as a prosthetic group model for the active site of five-coordinate hemoproteins. In the oxidized state a basic, a neutral or an acid form can be isolated. The basic and acid forms are monomeric at all concentrations. The neutral form is found dimeric in concentrated solutions while it is monomeric at low concentration. The coordination state of iron in these various species is investigated. The neutral form reacts with ligands, such as nitrogenous organic bases, leading to six-coordinate well-known hemichromes which exhibit low-spin electron spin resonance (ESR) spectra. The reaction of anionic ligands, such as F-, CN-, NO-2 and N-3, with the neutral form model leads to unsymmetrical six-coordinate complexes whose optical and ESR spectra are similar to those of synthetic deuteromyoglobin. In benzene, toluene or dichloromethane solutions iron (II)-deuteroporphyrin 6(7)-methyl ester, 7(6)-histidine methyl ester), obtained from ferric forms by heterogeneous reduction with aqueous dithionite, exhibits an optical spectrum characteristic of a five-coordinate high-spin ferrous complex. At low temperature important spectral modifications are observed indicating a dimeric association. At room temperature it binds one nitrogenous base molecule leading to the well-known hemochrome. It reacts also with carbon monoxide with a very high affinity constant (4.5 X 10(8) M-1), comparable to that of the isolated human hemoglobin alpha and beta chains, but much higher than the values reported for other various models, suggesting that the side-chain length bearing the fifth ligand may have an important influence upon the reactivity of the sixth position of the iron ion. At low temperature in toluene or dichloromethane, this compound reversibly binds oxygen without oxidation of the iron ion while oxidation occurs at room temperature. The significance of these results is discussed in relation with the local environment, the electronic nature of the base and the immobilization of the heme group in hemoproteins. (+info)
(5/1552) Reaction of the microsomal heme oxygenase with cobaltic protoporphyrin IX, and extremely poor substrate.
A reconstituted heme oxygenase system which was composed of a purified heme oxygenase from pig spleen microsomes and a partially purified NADPH-cytochrome c reductase from pig liver microsomes could not catalyze the conversion of cobaltic protoporphyrin IX (Co-heme) to biliverdin, although Co-heme could bind with the heme oxygenase protein to form a complex. The heme oxygenase system in the microsomes from pig spleen, rat spleen, and rat kidney also failed to oxidize Co-heme to biliverdin. Properties of the complex of Co-heme and heme oxygenase closely resembled those of cobalt myoglobin and cobalt hemoglobin; the Co-heme bound to the heme oxygenase protein did not react with cyanide and azide, the Co-heme moiety was reduced but only slowly with sodium dithionite, and the reduced form of the Co-heme did not appear to bind carbon monoxide. The co-heme bound to heme oxygenase was not reduced with the NADPH-cytochrome c reductase system in air. These findings further support the views that heme oxygenase may have a heme-binding crevice similar to those of myoglobin and hemoglobin and that reduction of heme is the prerequisite for the oxidative degradation of heme in the heme oxygenase reaction. (+info)
(6/1552) Optimum porphyrin accumulation in epithelial skin tumours and psoriatic lesions after topical application of delta-aminolaevulinic acid.
Photodynamic therapy with topically applied delta-aminolaevulinic acid is used to treat skin tumours by employing endogenously formed porphyrins as photosensitizers. This study examines the time course of porphyrin metabolite formation after topical application of delta-aminolaevulinic acid. Porphyrin biosynthesis in human skin tumours (basal cell carcinoma, squamous cell carcinoma), in psoriatic lesions, and in normal skin was investigated. Skin areas were treated with delta-aminolaevulinic acid, and levels of total porphyrins, porphyrin metabolites and proteins were measured in samples excised after 1, 2, 4, 6, 9, 12 and 24 h. There was an increase in porphyrin biosynthesis in all tissues with maximum porphyrin levels in tumours between 2 and 6 h and in psoriatic lesions 6 h after treatment. The pattern of porphyrins showed no significant difference between normal and neoplastic skin, protoporphyrin being the predominant metabolite. The results suggest that optimum irradiation time for superficial epithelial skin tumours may be as soon as 2 h after application of delta-aminolaevulinic acid, whereas for treatment of psoriatic lesions an application time of 6 h is more suitable. (+info)
(7/1552) Carbon monoxide stimulates the apical 70-pS K+ channel of the rat thick ascending limb.
We have investigated the expression of heme oxygenase (HO) in the rat kidney and the effects of HO-dependent heme metabolites on the apical 70-pS K+ channel in the thick ascending limb (TAL). Reverse transcriptase-PCR (RT-PCR) and Western blot analyses indicate expression of the constitutive HO form, HO-2, in the rat cortex and outer medulla. Patch-clamping showed that application of 10 microM chromium mesoporphyrin (CrMP), an inhibitor of HO, reversibly reduced the activity of the apical 70-pS K+ channel, defined by NPo, to 26% of the control value. In contrast, addition of 10 microM magnesium protoporphyrin had no significant effect on channel activity. HO involvement in regulation of the apical 70-pS K+ channel of the TAL, was further indicated by the addition of 10 microM heme-L-lysinate, which significantly stimulated the channel activity in cell-attached patches by 98%. The stimulatory effect of heme on channel activity was also observed in inside-out patches in the presence of 0.5-1 mM reduced nicotinamide adenine dinucleotide phosphate. This was completely abolished by 10 microM CrMP, suggesting that a HO-dependent metabolite of heme mediated the effect. This was further supported by exposure of the cytosolic membrane of inside-out patches to a carbon monoxide-bubbled bath solution, which increased channel activity. Moreover, carbon monoxide completely abolished the effect of 10 microM CrMP on the channel activity. In contrast, 10 microM biliverdin, another HO-dependent metabolite of heme, had no effect. We conclude that carbon monoxide produced from heme via an HO-dependent metabolic pathway stimulates the apical 70-pS K+ channel in the rat TAL. (+info)
(8/1552) A corrinoid-dependent catabolic pathway for growth of a Methylobacterium strain with chloromethane.
Methylobacterium sp. strain CM4, an aerobic methylotrophic alpha-proteobacterium, is able to grow with chloromethane as a carbon and energy source. Mutants of this strain that still grew with methanol, methylamine, or formate, but were unable to grow with chloromethane, were previously obtained by miniTn5 mutagenesis. The transposon insertion sites in six of these mutants mapped to two distinct DNA fragments. The sequences of these fragments, which extended over more than 17 kb, were determined. Sequence analysis, mutant properties, and measurements of enzyme activity in cell-free extracts allowed the definition of a multistep pathway for the conversion of chloromethane to formate. The methyl group of chloromethane is first transferred by the protein CmuA (cmu: chloromethane utilization) to a corrinoid protein, from where it is transferred to H4folate by CmuB. Both CmuA and CmuB display sequence similarity to methyltransferases of methanogenic archaea. In its C-terminal part, CmuA is also very similar to corrinoid-binding proteins, indicating that it is a bifunctional protein consisting of two domains that are expressed as separate polypeptides in methyl transfer systems of methanogens. The methyl group derived from chloromethane is then processed by means of pterine-linked intermediates to formate by a pathway that appears to be distinct from those already described in Methylobacterium. Remarkable features of this pathway for the catabolism of chloromethane thus include the involvement of a corrinoid-dependent methyltransferase system for dehalogenation in an aerobe and a set of enzymes specifically involved in funneling the C1 moiety derived from chloromethane into central metabolism. (+info)