Glutathione-dependent oxidative modification of protoporphyrin and other dicarboxylic porphyrins by mammalian and plant peroxidases.

Protoporphyrin, an intermediate in heme and chlorophyll biosynthesis, can accumulate in human and plant tissues under certain pathological conditions and is a photosensitizer used in cancer phototherapy. We previously showed that protoporphyrin and the related non-natural dicarboxylic porphyrin deuteroporphyrin are rapidly oxidized by horseradish peroxidase in the presence of some thiols, especially glutathione. This study reports that bovine lactoperoxidase, but not leucocyte myeloperoxidase, can also catalyze this reaction and that Tween and ascorbic acid are inhibitors. Exogenous hydrogen peroxide is not required and cannot replace glutathione. Deuteroporphyrin was oxidized to a unique green chlorin product with two oxygen functions added directly to the characteristic reduced pyrrole ring of the chlorin. Spectroscopic and chromatographic results suggest that protoporphyrin was oxidized not to a green chlorin, but to a much more polar red porphyrin modified by oxidative addition to the two vinyl side chains. Two related nonnatural dicarboxylic porphyrins, with ethyl or hydroxyethyl instead of vinyl side chains, are not substrates or products for this enzymatic conversion.     

NMR characterization of a diamagnetic model of unliganded alpha chains from human hemoglobin.

This paper reports the reconstitution and spectroscopic characterization of a complex between alpha globin from human adult hemoglobin and protoporphyrin IX-Zn(II). Optical and proton one-dimensional (1-D) NMR spectra indicate that the prosthetic group binds in a 1:1 stoichiometry to the apoglobin in a single conformation. Using 2-D proton NMR techniques we assigned resonances corresponding to the majority of porphyrin substituents and to several side chains of amino acids in contact with the porphyrin. Analysis of nuclear Overhauser enhancement interactions between identified protons indicated that the complex contains only one rotation isomer of the prosthetic group. The diamagnetic Zn(II) ion is coordinated to the proximal histidine (His87) and does not bind O2 or CO as a sixth ligand. The ring current effects on protons from the distal valine (Val62) are considerably higher than in the liganded form providing strong evidence for a more compact ligand binding pocket relative to the carbon monoxy state. Therefore, protoporphyrin-Zn(II)/alpha globin complex is a suitable diamagnetic model for unliganded alpha chains and will be used for structure determination by NMR and modeling methods.     

Enzymatic Activities for the Synthesis of Chlorophyll in Pigment-Deficient Variegated Leaves of Euonymus japonicus

The enzymes involved in the biosynthesis of chlorophyll (Chl)in pigment-deficient variegated leaves of Euonymus japonicuswere investigated. Each variegated leaf was composed of clearlydelineated green and white sectors. The white sectors containedalmost no Chls. The rate of synthesis of 5-aminolevulinic acid(ALA) in the white sectors in vivo was twice that in the greensectors. The level of glutamate 1-semialdehyde aminotransferasein the white sectors was much higher than that in the greensectors. Plastidic tRNA^Glu was also present at substantial levelsin the white sectors, indicating that the system for synthesisof ALA was very active in the white sectors. The activity of porphobilinogen (PBG) synthase in the whitesectors in vitro was twice that in the green sectors. In thewhite sectors the rate of porphyrin synthesis from PBG was 4-to 6-fold higher than in the green sectors. We measured Mg-chelataseactivity indirectly in both sectors by monitoring the accumulationof Mg-protoporphyrin IX in the presence of 2,2'-dipyridyl, whichinhibits isocyclic ring formation with the resultant accumulationof Mg-protoporphyrin IX. When sectors were incubated in darknesswith 2,2'-dipyridyl, large amounts of protoporphyrin IX accumulatedin the white sectors, whereas Mg-protoporphyrin IX mainly accumulatedin the green sectors. These results suggest that the enzymesfor the synthesis of porphyrin that catalyze conversion of ALAto protoporphyrin IX were very active and that the Mg-insertionstep might be blocked in the white sectors, with the resultantfailure to synthesize Chl. The deficiency is discussed in acomparison with that in other Chl-deficient plants. (Received November 15, 1995; Accepted March 21, 1996)     

Glutamyl-transfer RNA: a precursor of heme and chlorophyll biosynthesis.

In green plants, archaebacteria and many eubacteria, the porphyrin ring that is common to both chlorophyll and heme is synthesized from 5-aminolevulinic acid (ALA) via an interesting pathway. This two-step process involves the unusual enzymes glutamyl-tRNA reductase and glutamate-1-semialdehyde 2,1-aminomutase. Interest in this pathway has increased since it was discovered that a tRNA cofactor was required for the formation of ALA. This tRNA(Glu) is common to the biosyntheses of both porphyrins and proteins.     

Models for ferrous cytochrome b5: Sign inversions in the magnetic circular dichroism spectra of bis-imidazole ferrous porphyrin systems

The magnetic circular dichroism (MCD) spectrum of bis-imidazole ferrous tetraphenylporphyrin in the Soret region is nearly the mirror image of the spectrum of ferrous cytochrome b₅, a bis-imidazole (histidine)-ligated hemoprotein. Based on previous MCD studies of model and protein heme systems, a sign inversion in the spectra of two heme chromophores having essentially the same coordination structure is unexpected. To investigate whether the nature of the porphyrin itself could account for the observed spectral discrepancy, two additional model complexes, bis-imidazole ferrous protoporphyrin IX dimethylester and bis-imidazole ferrous octaethylporphyrin, whose peripheral porphyrin substituent patterns more closely match that of the protein- bound porphyrin, have been prepared and their MCD spectra measured. In these cases, the band pattern of the ferrous protein in the Soret region is successfully reproduced. It therefore appears that the anomalous MCD spectrum of the tetraphenylporphyrin complex can be attributed to the nature and positioning of the peripheral substituents on the porphyrin ring. Although iron tetraphenylporphyrin complexes are frequently used as models for protoporphyrin- containing hemoproteins, one should be aware that such differences in the peripheral porphyrin substituents may significantly affect the spectral properties of the model complex.     

Affinity chromatography of haemoproteins: 1. Synthesis of various imidazole containing matrices and their interaction with haemoglobin

The functional centre of haemoproteins is generally formed by an iron porphyrin and amino acid residues of he protein component. Some haemoproteins are able to bind imidazole to the iron of the prosthetic group. The synthesis of imidazole containing matrices is described and the affinity of haemoglobin as a model compound to these matrices has been studied. It was found that the lenght and structure of spacers as well as substituents at the imidazole ring are of critical importance: the adsorption of methaemoglobin shows two different kinds of protein matrix interaction: in case of a space length < 5 Å no interaction occurs for steric reasons; at a length > 5 Å adsorption takes place via complex formation between imidazole and iron of a prosthetic group independent of the linkage in 1- or 4(5)-position of the imidazole ring to the mtrix: the complex formation between imidazole and iron is the decisive step but is not solely responsible for the stability of the ocmplex: a hydroxyl group at the side chain near the imidazole decreases the adsorption drastically: large substituents at the imidazole ring disturb complex formation with the iron, but not the adsorption of haemoglobin; in the presence of a long spacer (> 20 A), hydrophobic interactions are predominantly responsible for the adsorption process and imidazole does not play any role.     

Raman characterization of human leukocyte myeloperoxidase and bovine spleen green haemoprotein. Insight into chromophore structure and evidence that the chromophores of myeloperoxidase are equivalent

Soret excitation resonance Raman spectroscopy has been used to characterize dimeric human leukocyte myeloperoxidase (donor:hydrogen peroxide oxidoreductase, EC 1.11.1.7) and monomeric bovine spleen green haemoprotein. The spectra of the two proteins, under the same conditions of iron valence and ligation, are essentially identical. Owing to strong symmetry reduction effects, the spectra are more complex than usually observed for haemoproteins. It is possible, however, to assign the high-frequency vibrations and, from these assignments, to determine structural features of the iron chromophores. In the resting protein, the iron adopts a six-coordinate high-spin configuration in both proteins; cyanide addition produces six-coordinate low-spin species, and in the ferrous enzymes the iron appears to be five-coordinate and high-spin. The proteins are stable to laser excitation and do not photoreduce under illumination. No evidence is found for unusual peripheral substituents, such as formyl or protonated Schiff's base group, in conjugation with the main chromophore in the native protein. The vibrational data are consistent with an iron chlorin chromophore, although other electronic effects, in addition to those produced by porphyrin ring reduction, are necessary to account for the optical properties of the proteins. The similarity in Raman spectra for myeloperoxidase and green haemoprotein indicates that the two iron sites in myeloperoxidase are equivalent.     

Oxidation of Methyl-Substituted Naphthalenes: Pathways in a Versatile Sphingomonas paucimobilis Strain

Aromatic compounds with alkyl substituents are abundant in fossil fuels. These compounds become important environmental sources of soluble toxic products, developmental inhibitors, etc. principally through biological activities. To assess the effect of methyl substitution on the completeness of mineralization and accumulation of pathway products, an isolate from a phenanthrene enrichment culture, Sphingomonas paucimobilis 2322, was used. Washed cell suspensions containing cells grown on 2,6-dimethylnaphthalene in mineral medium were incubated with various mono-, di-, and trimethylnaphthalene isomers, and the products were identified and quantified by gas chromatography and mass spectrometry. The data revealed enzymes with relaxed substrate specificity that initiate metabolism either by methyl group monoxygenation or by ring dioxygenation. Congeners with a methyl group on each ring initially hydroxylate a methyl, and this is followed by conversion to a carboxyl; when there are two methyl groups on a single ring, the first reaction is aryl dioxygenation of the unsubstituted ring. Intermediates are channeled to primary ring fission via dihydrodiols to form methyl-substituted salicylates. Further evidence that there are multiple pathways comes from the fact that both phthalate and (methyl)salicylate are formed from 2-methylnaphthalene.     

Formation of a complex of 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphyrin with G-quadruplex DNA

A water-soluble cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphyrin (TmPyP4), has been studied extensively because of its unique physicochemical properties that lead to interactions with nucleic acids, as well as its therapeutic application. Formation of a complex between TmPyP4 and parallel G-quadruplex DNA formed from a single repeat sequence of the human telomere, d(TTAGGG), has been characterized in an effort to elucidate the mode of molecular recognition between TmPyP4 and the DNA. The study demonstrated that TmPyP4 intercalates into the A3pG4 step of [d(TTAGGG)]4 with an association constant of 6.2 x 10(6) M(-1) and a stoichiometric ratio of 1:1. The binding of TmPyP4 to the A3pG4 step of [d(TTAGGG)]4 was found to be stabilized by the pi-pi stacking interaction of the porphyrin ring of TmPyP4 with the G4 quartet as well as the A3 bases of the G-quadruplex DNA. These findings provide novel insights for the design of porphyrin derivatives that bind to DNA with high affinity and specificity.     

Supramolecular chirality induction in bis(zinc porphyrin) by amino acid derivatives: rationalization and applications of the ligand bulkiness effect

The achiral syn conformer (face-to-face) of the ethane-bridged bis(zinc porphyrin) (syn-ZnD) transforms into the corresponding chiral extended anti bis-ligated species (anti-ZnD.L2) in the presence of enantiopure ligands (L: amino acid derivatives). The mechanism of the supramolecular chirality induction is based on chiral ligand binding to zinc porphyrins and subsequent formation of either right- or left-handed screw structures in anti-ZnD.L2. The screw structure formation arises from steric interactions between the bulkiest substituent at the asymmetric carbon of the ligand and the peripheral ethyl groups of the neighboring porphyrin ring directed towards the covalent bridge. The sign and amplitude of the induced circular dichroism (CD) are dependent on the steric bulk of the substituents at the chiral center. The greater difference in size between the chiral center's substituents gives the stronger induced CD signal. Rationalization of the ligand bulkiness effect on chirality induction by amino acid derivatives, application of this supramolecular system for the determination of ligand absolute configuration, and relative bulkiness of the substituents at the asymmetric carbon are discussed.     

The role of carboxymethyl substituents in the interaction of tetracationic porphyrins with DNA

Cationic porphyrin-based compounds capable of interacting with DNA are currently under extensive investigation as prospective anticancer and anti-infective drugs. One of the approaches to enhancing the DNA-binding affinity of these ligands is chemical modification of functional groups of the porphyrin macrocycle. We analyzed the interaction with DNA of novel derivatives containing carboxymethyl and ethoxycarbonylmethyl substituents at quaternary nitrogen atoms of pyridinium groups at the periphery of the porphyrin macrocycle. The parameters of binding of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium)porphyrin (P1) and 5,10,15,20-tetrakis(N-ethoxycarbonylmethyl-4-pyridinium)porphyrin (P2) to double-stranded DNA sequences of different nucleotide content were determined using optical spectroscopy. The association constant of P1 interaction with calf thymus DNA (K?=?3.4?×?10(6)?M(-1)) was greater than that of P2 (K?=?2.8?×?10(5)?M(-1)). Preferential binding of P1 to GC- rather than AT-rich oligonucleotides was detected. In contrast, P2 showed no preference for particular nucleotide content. Modes of binding of P1 and P2 to GC and AT duplexes were verified using the induced circular dichroism spectra. Molecular modeling confirmed an intercalative mode of interaction of P1 and P2 with CpG islands. The carboxyl groups of the peripheral substituent in P1 determine the specific interactions with GC-rich DNA regions, whereas ethoxycarbonylmethyl substituents disfavor binding to DNA. This study contributes to the understanding of the impact of peripheral substituents on the DNA-binding affinity of cationic porphyrins, which is important for the design of DNA-targeting drugs.     

Interactions of water soluble porphyrins with Z-poly(dG-dC).

The water soluble porphyrin tetrakis(4-N-methylpyridyl)porphine (H2TMpyP) and its copper(II) derivative (CuTMpyP) convert Z-poly(dG-dC) to the B-form. For H2TMpyP, the fraction Z character (fr-Z) is given by fr-Z = 1.0 - 21 rO and for CuTMpyP, fr-Z = .94 - 12 rO where rO identical to [Porphyrin]O/[DNA]O. Neither the manganese(III) derivative of of this porphyrin (MnTMpyP) nor tetrakis(2-N-methylpyridyl)porphine (H2TMpyP-2) is nearly as effective at causing the conversion. The former two porphyrins have been shown to intercalate into B-poly(dG-dC) whereas the latter two porphyrins do not. The kinetics of the Z----B conversion are independent of porphyrin or poly(dG-dC) concentration for 1/rO greater than 6. At smaller values of 1/rO, the conversion rate is greatly increased for H2TMpyP and CuTMpyP. The interaction of these porphyrins with Z-poly(dG-dC) follows simple first order kinetics in this latter concentration range. It is proposed that for small values of 1/rO the sequence of events begins with a porphyrin-unassisted distortion of the Z-duplex (with a rate constant of 0.6 s-1) followed by a rapid uptake of porphyrin in what may be an intercalative mode. The porphyrin thus located in Z-regions brings about rapid conversion to the B-form. Binding of H2TMpyP or CuTMpyP to B-regions of a predominantly Z-strand leads to conversion of Z to B. However, this conversion process is considerably slower than when the porphyrins bind directly to Z-regions.     

Protein influences on porphyrin structure in cytochrome c: evidence from Raman difference spectroscopy

To probe the details of protein heme interactions, we have developed a Raman difference spectroscopic technique, which allows reliable detection of very small, approximately equal to 0.01 cm-1, frequency differences. When this technique is applied to heme proteins, structural differences in the protein which perturb the porphyrin macrocycle may be examined by obtaining Raman difference data on the porphyrin vibrational modes which are strongly enhanced in the Raman spectrum produced with visible laser excitation. We report here Raman difference spectroscopic data on cytochromes c from 24 species. The differences in the Raman spectrum of the porphyrin between the cytochromes c of any two species are small, confirming that all of the cytochromes we have examined have the same "cytochrome fold". However, many small (0.02-2 cm-1) but systematic differences were detected which indicate structural differences among these proteins. These differences could be classified into three different groups and interpreted in terms of different types of structural variations resulting from specific differences in the amino acid sequences. First, direct interactions between near-heme residues and the porphyrin influence the electron density in the pi orbitals of the porphyrin macrocycle. Second, variation in the residue at position 92, far removed from the heme, affects the frequency of the core-size marker line at 1584 cm-1. Third, the conformation near cysteine 14 affects the shape of the Raman mode which is sensitive to the pyrrole ring substituents (approximately 1313 cm-1). From these data we conclude that there are several ways in which the protein amino acid sequence may regulate the oxidation-reduction potential and several ways in which the sequence can modify the binding site between cytochrome c and its redox partners.     

Lactones 35 [1]. Metabolism of iodolactones with cyclohexane ring in Absidia cylindrospora culture

The metabolism of δ-iodo-γ-lactones containing cyclohexane ring with an increasing number of methyl substituents in Absidia cylindrospora was studied and seven metabolites were isolated as the products of biotransformations of these substrates. They were formed as the result of various dehalogenation pathways and four of them (hydroxylactones and epoxylactone) turned out to be new compounds. The conversion of substrates ranged from 60% to 90% and the highest conversion was observed for the iodolactone with an unsubstituted cyclohexane ring. The products were fully characterized by the spectroscopic methods and for the hydroxylactone with gem-dimethyl group at C-5 and hydroxylactone with trimethylcyclohexane system the crystal structures were obtained. The main products formed in the process of hydrolytic dehalogenation were δ-hydroxy-γ-lactones with the hydroxy group located cis in relation to lactone moiety. In case of lactone with 4,4,6-trimethylcyclohexane system the dehydrohalogenation followed by the epoxidation of double bond was also observed. One of the metabolites 4,5-epoxy-2,2,6-trimethyl-9-oxabicyclo[4.3.0]nonan-8-one was formed in the sequence of three reactions: hydroxylation at C-5, translactonization and intramolecular nucleophilic substitution of the iodine by the hydroxy group. Some of the isolated products of transformation of the iodolactone with trimethylcyclohexane system were obtained as the single enantiomers. The application of fungi studied to the dehalogenation of iodolactones could be a useful method in the production of new metabolites with oxygen-containing functional groups with antifeedant activity.     

The effect of ruthenium on the performance of porphyrin dye and porphyrin–fullerene dyad solar cells predicted by DFT and TD-DFT calculations

The effect of ruthenium on the performance of porphyrin dye and porphyrin–fullerene (PF) dyad solar cells is investigated by using density functional theory and time-dependant density functional theory calculations. The results reveal that ruthenium facilitates rapid electron injection from porphyrin to fullerene, narrows the band gaps of porphyrin dye and PF dyad and alters the density of states near the corresponding Fermi levels. The HOMOs are localised on the donor moieties and the LUMOs on the acceptor moieties. The donor and acceptor dyads form good donor–acceptor pairs for photo-to-current conversion under the effect of ruthenium. HOMOs of porphyrin and ruthenium metalloporphyrin dyes fall within the (TiO₂)₆₀ and Ti₃₈O₇₆ gaps, and support the issue of typical interfacial electron transfer reaction. The calculated transition energies of porphyrin are almost insensitive to ethanol solvent effects. The introduction of ruthenium to the porphyrin ring leads to more active nonlinear optical performance, stronger response to the external electric field and induces higher photo-to-current conversion efficiency. Moreover, ruthenium shifts the absorption bands of porphyrin and makes it a potential candidate for harvesting light for photovoltaic applications.     

The importance of porphyrin distortions for the ferrochelatase reaction

Ferrochelatase is the terminal enzyme in haem biosynthesis, i.e. the enzyme that inserts a ferrous ion into the porphyrin ring. Suggested reaction mechanisms for this enzyme involve a distortion of the porphyrin ring when it is bound to the enzyme. We have examined the energetics of such distortions using various theoretical calculations. With the density functional B3LYP method we calculate how much energy it costs to tilt one of the pyrrole rings out of the porphyrin plane for an isolated porphyrin molecule without or with a divalent metal ion in the centre of the ring. A tilt of 30 degrees costs 65-130 kJ/mol for most metal ions, but only approximately 48 kJ/mol for free-base (neutral) porphine. This indicates that once the metal is inserted, the porphyrin becomes stiffer and flatter, and therefore binds with lower affinity to a site designed to bind a distorted porphyrin. This would facilitate the release of the product from ferrochelatase. This proposal is strengthened by the fact that the only tested metal ion with a lower distortion energy than free-base porphyrin (Cd(2+)) is an inhibitor of ferrochelatase. Moreover, it costs even less energy to tilt a doubly deprotonated porphine(2-) molecule. This suggests that the protein may lower the acid constant of the pyrrole nitrogen atoms by deforming the porphyrin molecule. We have also estimated the structure of the protoporphyrin IX substrate bound to ferrochelatase using combined quantum chemical and molecular mechanics calculations. The result shows that the protein may distort the porphyrin by approximately 20 kJ/mol, leading to a distinctly non-planar structure. All four pyrrole rings are tilted out of the porphyrin mean plane (1-16 degrees ) but most towards the putative binding site of the metal ion. The predicted tilt is considerably smaller than that observed in the crystal structure of a porphyrin inhibitor.     

Reactions of manganese porphyrins with peroxynitrite and carbonate radical anion

We have studied the reaction kinetics of ten manganese porphyrins, differing in their meso substituents, with peroxynitrite (ONOO-) and carbonate radical anion (CO3.) using stopped-flow and pulse radiolysis, respectively. Rate constants for the reactions of Mn(III) porphyrins with ONOO- ranged from 1 x 10(5) to 3.4 x 10(7) m(-1) s(-1) and correlated well with previously reported kinetic and thermodynamic data that reflect the resonance and inductive effects of the substituents on the porphyrin ring. Rate constants for the reactions of Mn(III) porphyrins with CO3. ranged from 2 x 10(8) to 1.2 x 10(9) m(-1)s(-1) at pH 相似文献   

Interactions of DNA with a new electron-deficient tentacle porphyrin: meso-Tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine)phenyl]porphyrin

A new electron-deficient tentacle porphyrin meso-tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine)phenyl]porphyrin (TθF₄TAP) has been synthesized. The binding interactions of TθF₄TAP with DNA polymers were studied for comparison to those of an electron-deficient tentacle porphyrin and an electron-rich tentacle porphyrin; these previously studied porphyrins bind to DNA primarily by intercalative and outside-binding modes, respectively. The three tentacle porphyrins have similar size and shape. The basicity of TθF₄TAP indicated that it has electronic characteristics similar to those of the intercalating electron-deficient tentacle porphyrin. However, TθF₄TAP binds to calf thymus DNA, [poly(dA-dT)]₂, and [poly(dG-dC)]₂ in a self-stacking, outside-binding manner under all conditions. Evidence for this binding mode included a significant hypochromicity of the Soret band, a conservative induced CD spectrum, and the absence of an increase in DNA solution viscosity. As found previously for the electron-rich porphyrin, the results suggest that combinations of closely related self-stacked forms coexist. The mix of forms depended on the DNA and the solution conditions. There are probably differences in the detailed features of the self-stacking adducts for the two types of tentacle porphyrins, especially at high R (ratio of porphyrin to DNA). At low R values, the induced CD signal of TθF₄TAP/CT DNA resembled that of TθF₄TAP/[poly(dA-dT)]₂, suggesting that TθF₄TAP binds preferentially at AT regions. Competitive binding experiments gave evidence that TθF₄TAP binds preferentially to [poly(dA-dT)]₂ over [poly(dG-dC)]₂. Thus, despite the long, positively charged, flexible substituents on the porphyrin, the binding of TθF₄TAP is significantly affected by base-pair composition. Similar characteristics were found previously for the electron-rich tentacle porphyrin. Thus, significant changes in electron richness have relatively minor effects on this outside binding selectivity for AT regions. TθF₄TAP is the first porphyrin with electron deficiency and shape similar to intercalating porphyrins that does not appear to intercalate. All porphyrins reported to intercalate have had pyridinium substituents. Thus, the electronic distribution in the porphyrin ring, not just the overall electron richness, may play a role in facilitating intercalation. © 1997 John Wiley & Sons, Inc. Biopoly 42: 203–217, 1997     

Magnetic resonance studies of the binding of 13C-labeled carbon monoxide to myoglobins and hemoglobins containing modified hemes.

The effects of changes in the groups attached to the periphery of the porphyrin ring of the heme of various hemoglobin and myoglobins on the environment experienced by the ligand, carbon monoxide, have been studied by observation of the chemical shift of the bound 13CO. The results indicate that the major interaction between bound ligands and substituents around the porphyrin is that transmitted electronically from substituent to ligand. The nature of the protein environment around the ligand and the interaction between the proximal histidine (F8) and the ligand (through the iron atom) impose differences between subunits of hemoglobin and between myoglobins and hemoglobins which are largely, but not entirely, independent of these substituent effects. To assess the influence of protein structure on the chemical shifts of bound ligand, the shifts of 13CO bound to myoglobin and hemoglobins from a wide range of species have also been measured.     

A nuclear magnetic resonance study of the interactions of antimalarial drugs with porphyrins

Haematins (hydroxyferriprotoporphyrin IX) constitute a possible receptor for antimalarial drugs such as chloroquine or quinine. This paper reports the study of the interactions of these two molecules with two tetrapyrrole (haematin and uroporphyrin I) by 1H-NMR spectroscopy. This method provided us with the geometry of the interactions in aqueous medium. The interaction consists of a close stacking of the porphyrin ring and the quinoleine moiety of the drugs. Using a porphyrin ring current model it was possible to reach the spatial relationships of the interacting species. It was concluded that hydrophobic forces play a key role in the interaction. The porphyrin plane can accommodate wide structural variations of the interacting species, leading to a weak specificity. The consequences on the mode of action of antimalarial drugs are discussed.