Crystal structures and calorimetry reveal catalytically relevant binding mode of coproporphyrin and coproheme in coproporphyrin ferrochelatase

Coproporphyrin ferrochelatases (CpfCs, EC 4.99.1.9) insert ferrous iron into coproporphyrin III yielding coproheme. CpfCs are utilized by prokaryotic, mainly monoderm (Gram-positive) bacteria within the recently detected coproporphyrin-dependent (CPD) heme biosynthesis pathway. Here, we present a comprehensive study on CpfC from Listeria monocytogenes (LmCpfC) including the first crystal structure of a coproheme-bound CpfC. Comparison of crystal structures of apo-LmCpfC and coproheme-LmCpfC allowed identification of structural rearrangements and of amino acids involved in tetrapyrrole macrocycle and Fe2+ binding. Differential scanning calorimetry of apo-, coproporphyrin III-, and coproheme-LmCpfC underline the pronounced noncovalent interaction of both coproporphyrin and coproheme with the protein (ΔTm  = 11 °C compared to apo-LmCpfC), which includes the propionates (p2, p4, p6, p7) and the amino acids Arg29, Arg45, Tyr46, Ser53, and Tyr124. Furthermore, the thermodynamics and kinetics of coproporphyrin III and coproheme binding to apo-LmCpfC is presented as well as the kinetics of insertion of ferrous iron into coproporphyrin III-LmCpfC that immediately leads to formation of ferric coproheme-LmCpfC (kcat /KM  = 4.7 × 105  m-1 ·s-1 ). We compare the crystal structure of coproheme-LmCpfC with available structures of CpfCs with artificial tetrapyrrole macrocycles and discuss our data on substrate binding, iron insertion and substrate release in the context of the CPD heme biosynthesis pathway. ENZYME: EC 4.99.1.9 DATABASE: pdb-codes of structural data in this work: 6RWV, 6SV3.

Separation and fragmentation study of isocoproporphyrin derivatives by UHPLC-ESI-exact mass MS/MS and identification of a new isocoproporphyrin sulfonic acid metabolite

Isocoproporphyrin and its derivatives are commonly used as biomarkers of porphyria cutanea tarda, heavy metal toxicity and hexachlorobenzene (HCB) intoxication in humans and animals. However, most are isobaric with other porphyrins and reference materials are unavailable commercially. The structural characterisation of these porphyrins is important but very little data is available. We report here the separation and characterisation of isocoproporphyrin, deethylisocoproporphyrin, hydroxyisocoproporphyrin and ketoisocoproporphyrin, isolated in the faeces of rats fed with a diet containing HCB, by ultra high performance liquid chromatography-exact mass tandem mass spectrometry (UHPLC-MS/MS). Furthermore, we report the identification and characterisation of a previously unreported porphyrin metabolite, isocoproporphyrin sulfonic acid isolated in the rat faeces. The measured mass-to-charge ratio (m/z) of the precursor ion was m/z 735.2338, corresponding to a molecular formula of C36H39N4O11S with an error of 0.3 ppm from the calculated m/z 735.2336. The MS/MS data was consistent with an isocoproporphyrin sulfonic acid structure, derived from dehydroisocoproporphyrinogen by sulfonation of the vinyl group. The metabolite was present in a greater abundance than other isocoproporphyrin derivatives and may be a more useful biomarker for HCB intoxication.

Histamine interaction with Zn2+ and Cu2+ porphyrins

Histamine may be present in biological fluids and in pharmaceutical dosage forms such as antiallergenic agents; when in excess, it causes a disorder called histaminosis. Many techniques have been developed to determine the concentration of this compound but the application of such methods is complicated and laborious, requiring expensive equipment and long times. A better alternative is to design chemical sensors. In the work reported here, six metalloporphyrins (Cu2+ or Zn2+) with different peripheral groups - benzoate, tosylate and carboxylate - were studied. The stability constants for these compounds were determined with histamine at different temperatures. Histamine is strongly bound to metallic porphyrins containing Cu2+ and Zn2+; however, the binding force does not depend exclusively on the metal center. Stabilization of the complex is strongly influenced, in some cases, by the lateral chains of the porphyrin. This possibility implies that this system can be very selective for this biogenic amine.

Identification of tetrapyrrole compounds excreted by Rhodobacter sphaeroides and sources of the methyl hydrogens of bacteriochlorophyll a biosynthesized by R. sphaeroides, based on 13C-NMR spectral analysis of coproporphyrin III tetramethyl ester

Red-fluorescent tetrapyrrole compounds excreted by Rhodobacter sphaeroides into the culture broth were concluded to be coproporphyrinogen (Copro'gen) III and uroporphyrinogen (Uro'gen) I, based on the (13)C-NMR spectral identification of coproporphyrin (Copro) III tetramethyl ester and uroproporphyrin (Uro) I octamethyl ester. The sources of the methyl hydrogens of bacteriochlorophyll a were established by analysis of the (13)C-NMR spectra of (2)H,(13)C-Copro III tetramethyl ester chemically derived from (2)H,(13)C-Copro'gen III biosynthesized through the feeding of delta-amino[2-(13)C]levulinic acid (ALA) to R. sphaeroides in medium containing 50% (2)H(2)O. We confirmed the previous finding that one of the methyl hydrogens was derived from water in the medium during decarboxylation of four acetyl side chains of Uro'gen III to generate Copro'gen III. It was further shown that the other hydrogen atoms, previously reported to be derived from methylene hydrogens at C-2 of ALA, had been exchanged with hydrogen of water in the medium in the biosynthetic pathways leading from ALA to Copro'gen III.

De novo Design of ?F -containing Heme-binding Peptides

The structural characterization of de novo designed metalloproteins together with determination of chemical reactivity can provide a detailed understanding of the relationship between protein structure and functional properties. Toward this goal, using the basic scaffold of 1pbz (Rosenblatt et al. (2003) Proc Natl Acad Sci U S A;100:13140) we have designed cyclic DeltaF-containing heme-binding peptides. The alpha- and beta-bands in UV-Vis spectroscopy are indicative of bis-His-ligated heme complex. Most of our DeltaF-containing peptides have more affinity to cobalt(III)Coproporphyrinate-I than heme because cobalt(III)Coproporphyrinate-I contains two additional propionate groups which can have salt bridge interactions with the lysine residues in the peptide. Helicity induction in peptide by DeltaF and aromatic interaction of DeltaF with heme have increased the heme affinity of CP-6-12pbz (cyclic peptide with substitutions of Ala at positions 6 and 12 by DeltaF; 905/mm) compared with 1pbz (279/mm). The nuclear magnetic resonance spectra are indicative of overall helical structure for CP-6-12pbz and CP-6-12pbz in complex with cobalt (III)Coproporphyrinate-I. The descending order of heme affinity in peptides (CP-6-12pbz > CP-12pbz > CP-5-12pbz) indicates that DeltaF at i + 3 or i - 3 from the central H9 favors heme binding but disrupts the same when placed at i - 4.

The Influence of Aggregation of Porphyrins on the Efficiency of Photogeneration of Hydrogen Peroxide in Aqueous Solution

The pH-dependence of the ability of coproporphyrin (CP) and uroporphyrin (UP) to photogenerate hydrogen peroxide (H2O2) in aqueous solution was investigated, with special attention to the structure-activity relationship related to the aggregation of the porphyrins. It was found that the efficiency was strongly dependent on the aggregation of CP and UP mediated by changes in the pH of the solution, and a dimeric form had a weak ability to produce H2O2, while a highly aggregated form had a good ability. The increased efficiency of the highly aggregated porphyrin to produce H2O2 was further demonstrated using a different type of aggregate formed by the electrostatic interaction of cationic tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphin (TMPyP) with anionic tetrakis-5,10,15,20-(4-sulfonatophenyl)porphin (TSPP). The present results demonstrated the importance of the state of aggregation of porphyrin to photogenerate H2O2, and the results may help to develop a new type of medicine for photodynamic therapy.

Metabolism of pentacarboxylate porphyrinogens by highly purified human coproporphyrinogen oxidase: Further evidence for the existence of an abnormal pathway for heme biosynthesis

An abnormal series of porphyrin tetracarboxylic acids known as the isocoproporphyrins, are commonly excreted by patients suffering from the disease porphyria cutanea tarda (PCT). These porphyrins appear to arise by bacterial degradation of dehydroisocoproporphyrinogen that is generated by the premature metabolism of the normal pentacarboxylate intermediate (5dab) by coproporphyrinogen oxidase (copro'gen oxidase). This porphyrinogen can be further metabolized by uroporphyrinogen decarboxylase to give harderoporphyrinogen, one of the usual intermediates in heme biosynthesis. Therefore, it is possible that some of the heme formed under abnormal conditions may originate from the 'isocopro-type' porphyrinogen intermediate. In order to investigate the feasibility of alternative pathways for heme biosynthesis, the four type III pentacarboxylate isomeric porphyrinogens were incubated with purified, cloned human copro'gen oxidase at 37 degrees C with various substrate concentrations under initial velocity conditions. Of the four isomers, only 5dab was a substrate for copro'gen oxidase and this gave dehydroisocoproporphyrin. The structure of the related porphyrin tetramethyl ester was confirmed by proton NMR spectroscopy and mass spectrometry. The K(m) value for proto'gen-IX formation from copro'gen, an indicator of molecular recognition, was similar to the K(m) value for monovinyl product formation with 5dab, although copro'gen-III has an approximately twofold higher K(cat) value. Although 5dab is a slightly poorer substrate than copro'gen-III, these results support the hypothesis that an abnormal route for heme biosynthesis is possible in humans suffering from PCT or related syndromes such as hexachlorobenzene poisoning.

Homogeneous assays for cellular proteases employing the platinum(II)–coproporphyrin label and time-resolved phosphorescence

Phosphorescent platinum(II) coproporphyrin label (PtCP) is evaluated for the detection of cellular proteases by time-resolved fluorescence in homogeneous format. An octameric peptide containing the recognition motif for the caspase-3 enzyme was dual labeled with a new maleimide derivative of PtCP and with the dark quencher dabcyl. Following photophysical characterization, the quenched substrate was employed in cleavage assays for caspase-3 using Jurkat and HL60 cell lines treated with proapoptotic stimuli performed on a commercial plate reader. Dose-response and time course assays for the drug camptothecin were obtained for comparison with conventional fluorometric detection.

Production of singlet oxygen on irradiation of a photodynamic therapy agent, zinc-coproporphyrin III, with low host toxicity

Zinc-coproporphyrin III (Zincphyrin) acts efficiently as a photodynamic therapy (PDT) agent in mice, while it shows no tumor cell-killing activity in vitro and has a high LD50 (low toxicity) in mice. It appears to have advantages over other porphyrins as a practical PDT reagent. In order to examine the action mechanism of Zincphyrin in PDT, we evaluated the photochemical characteristics of Zincphyrin by measurement of the near-infrared emission at 1268 nm, which provides direct evidence for formation of 1O2. Intense emission was observed in the presence of Zincphyrin, and was completely inhibited by NaN3, a 1O2 scavenger. Based on a quenching study, the rate constant of the reaction of 1O2 with NaN3 was determined to be 1.5-3.5 M(-1) s(-1), which is close to the reported value (3.8 x 10(8) M(-1) s(-1)). The intensity of the 1O2-specific emission was proportional to both the laser power and the concentration of Zincphyrin. The fluorescence quantum yield of Zincphyrin was 0.004 in phosphate buffer (100 mM, pH 7.4), which indicates that the excited state decays via other pathway(s) faster than through the fluorescence emission pathway. The lifetime of the triplet state of Zincphyrin (210 micros) was relatively long compared to that of other porphyrins, such as hematoporphyrin (Hp) (40 micros), coproporphyrin I (50 gs), or coproporphyrin III (36 gs). These results demonstrate the photodynamic generation of 1O2 by Zincphyrin.

Evaluation of the phosphorescent palladium(II)-coproporphyrin labels in separation-free hybridization assays

Palladium(II)-coproporphyrin label and a set of corresponding monofunctional labeling reagents with different linker arms were evaluated for labeling of oligonucleotides and subsequent use in hybridization assays. The properties of resulting oligonucleotide probes including phosphorescence spectra, quantum yields, lifetimes, and labeling yields were examined as functions of the label and oligonucleotide structures. Upon hybridization with complementary sequences bearing dabcyl, QSY-7, and rhodamine green dyes, the probes displayed strong quenching due to close proximity effects. Intensity and lifetime changes of the phosphorescence, distance, and temperature dependences were investigated in detail. The potential of the new label and probes for sensitive and separation-free hybridization assays was discussed.

Conformational dynamics and temperature dependence of photoinduced electron transfer within self-assembled coproporphyrin:cytochrome c complexes

The focus of the present study is to better understand the complex factors influencing intermolecular electron transfer (ET) in biological molecules using a model system involving free-base coproporphyrin (COP) complexed with horse heart cytochrome c (Cc). Coproporphyrin exhibits bathochromic shifts in both the Soret and visible absorption bands in the presence of Cc and an absorption difference titration reveals a 1:1 complex with an association constant of 2.63 +/- 0.05 x 10(5) M(-1). At 20 degrees C, analysis of time-resolved fluorescence data reveals two lifetime components consisting of a discrete lifetime at 15.0 ns (free COP) and a Gaussian distribution of lifetimes centered at 2.8 ns (representing (1)COP --> Cc ET). Temperature-dependent, time-resolved fluorescence data demonstrate a shift in singlet lifetime as well as changes in the distribution width (associated with the complex). By fitting these data to semiclassical Marcus theory, the reorganizational energy (lambda) of the singlet state electron transfer was calculated to be 0.89 eV, consistent with values for other porphyrin/Cc intermolecular ET reactions. Using nanosecond transient absorption spectroscopy the temperature dependences of the forward and thermal back ET originating from triplet state were examined ((3)COP --> Cc ET). Fits of the temperature dependence of the rate constants to semiclassical Marcus theory gave lambda of 0.39 eV and 0.11 eV for the forward and back triplet ET, respectively (k(f) = (7.6 +/- 0.3) x 10(6) s(-1), k(b) = (2.4 +/- 0.3) x 10(5) s(-1)). The differing values of lambda for the forward and back triplet ET demonstrate that these ET reactions do not occur within a static complex. Comparing these results with previous studies of the uroporphyrin:Cc and tetrakis (4-carboxyphenyl)porphyrin:Cc complexes suggests that side-chain flexibility gives rise to the conformational distributions in the (1)COP --> Cc ET whereas differences in overall porphyrin charge regulates gating of the back ET reaction (reduced Cc --> COP(+)).

Influence of linker unit on performance of palladium(II) coproporphyrin labelling reagent and its bioconjugates

In this paper we describe the preparation of a series of new phosphorescent labelling reagents, based on monosubstituted palladium(II) coproporphyrin-I and the isothiocyanato reactive group. The labelling reagents differ with respect to the chemical composition of the linker unit that combines the reactive group and the porphyrin chromophore. Altogether, seven different labelling reagents are prepared. The new labelling reagents are conjugated with monoclonal mouse IgG to yield label conjugates with variable degrees of conjugation. The effect is studied of linker unit on: (a) the conjugation reaction kinetics; (b) the biological activity of the resulting IgG conjugates; and (c) the efficiency of phosphorescence emission. The results show that an increase in the length of the linker unit has a positive effect on both the reactivity of the label and the biological activity of the resulting conjugates. In addition, the results indicate that the labels with the most hydrophilic linker units exhibit the highest phosphorescence emission efficiencies.

A description of an HPLC assay of coproporphyrinogen III oxidase activity in mononuclear cells

Coproporphyrinogen III oxidase is deficient in hereditary coproporphyria. An activity assay for this enzyme in mononuclear cells, besides the preparation of the substrate, are presented. The separation conditions for the product of the test protoporphyrin IX by gradient, reversed-phase high-performance liquid chromatography are given. The normal value from mononuclear cells of healthy volunteers was 138 +/- 21 pkat/g total soluble protein (mean +/- SD). The enzyme activity of a family with hereditary coproporphyria was measured. The gene carriers exhibit a specific coproporphyrinogen III oxidase activity of 61-90 pkat/g total soluble protein.

Phosphorescent metalloporphyrins as labels in time-resolved luminescence microscopy: effect of mounting on emission intensity

In this study, we present an investigation of the effects of mounting media on the phosphorescence of metalloporphyrin stained microscopy samples. The samples were: (1) Platinum(II) coproporphyrin (=PtCP) stained porous Sephadex beads; (2) compact polystyrene microspheres coated with IgG-PtCP conjugate; and (3) immunocytochemically labeled human peripheral blood neutrophils. The human neutrophils in a mixed leukocyte population were fixed, permeabilized, and then immunolabeled with PtCP conjugate of monoclonal mouse IgG directed to the intracellular antigen myeloperoxidase. The samples were mounted in twelve different mounting media and studied with quantitative time-resolved luminescence imaging microscopy with respect to the intensity and stability of the phosphorescence signal. The results indicate that microscopy samples stained with PtCP exhibit the brightest phosphorescence emission in non-mounted form or when mounted in non-aqueous permanent mounting media.

[Biosynthesis and use of coproporphyrins and uroporphyrins and their metal complexes in immune analysis and diagnostic methods]

Methods of synthesis of coproporphyrin and uroporphyrin by using bacteria of the genus Arthrobacter are proposed. Metal complexes of coproporphyrin and uroporphyrin with Pt, Pd, and Zn were synthesized. Their structures were identified by spectrophotometry, IR spectrometry, 1H-NMR, mass spectrometry, and HPLC. Data showing the possibility to use coproporphyrin III-metal complexes as luminophores for fluorescence detection of tumors. The current and prospective uses of metal complexes of water-soluble natural porphyrins in advanced immunofluorescence assays are discussed.

Extracellular heme peroxidases in actinomycetes: a case of mistaken identity

Actinomycetes secrete into their surroundings a suite of enzymes involved in the biodegradation of plant lignocellulose; these have been reported to include both hydrolytic and oxidative enzymes, including peroxidases. Reports of secreted peroxidases have been based upon observations of peroxidase-like activity associated with fractions that exhibit optical spectra reminiscent of heme peroxidases, such as the lignin peroxidases of wood-rotting fungi. Here we show that the appearance of the secreted pseudoperoxidase of the thermophilic actinomycete Thermomonospora fusca BD25 is also associated with the appearance of a heme-like spectrum. The species responsible for this spectrum is a metalloporphyrin; however, we show that this metalloporphyrin is not heme but zinc coproporphyrin. The same porphyrin was found in the growth medium of the actinomycete Streptomyces viridosporus T7A. We therefore propose that earlier reports of heme peroxidases secreted by actinomycetes were due to the incorrect assignment of optical spectra to heme groups rather than to non-iron-containing porphyrins and that lignin-degrading heme peroxidases are not secreted by actinomycetes. The porphyrin, an excretory product, is degraded during peroxidase assays. The low levels of secreted peroxidase activity are associated with a nonheme protein fraction previously shown to contain copper. We suggest that the role of the secreted copper-containing protein may be to bind and detoxify metals that can cause inhibition of heme biosynthesis and thus stimulate porphyrin excretion.

Proof of principle in a de novo designed protein maquette: an allosterically regulated, charge-activated conformational switch in a tetra-alpha-helix bundle

New understanding of the engineering and allosteric regulation of natural protein conformational switches (such as those that couple chemical and ionic signals, mechanical force, and electro/chemical free energy for biochemical activation, catalysis, and motion) can be derived from simple de novo designed synthetic protein models (maquettes). We demonstrate proof of principle of both reversible switch action and allosteric regulation in a tetra-alpha-helical bundle protein composed of two identical di-helical subunits containing heme coordinated at a specific position close to the disulfide loop region. Individual bundles assume one of two switch states related by large-scale mechanical changes: a syn-topology (helices of the different subunits parallel) or anti-topology (helices antiparallel). Both the spectral properties of a coproporphyrin probe appended to the loop region and the distance-dependent redox interaction between the hemes identify the topologies. Beginning from a syn-topology, introduction of ferric heme in each subunit (either binding or redox change) shifts the topological balance by 25-50-fold (1.9-2.3 kcal/mol) to an anti-dominance. Charge repulsion between the two internal cationic ferric hemes drives the syn- to anti-switch, as demonstrated in two ways. When fixed in the syn-topology, the second ferric heme binding is 25-80-fold (1.9-2.6 kcal/mol) weaker than the first, and adjacent heme redox potentials are split by 80 mV (1.85 kcal/mol), values that energetically match the shift in topological balance. Allosteric and cooperative regulation of the switch by ionic strength exploits the shielded charge interactions between the two hemes and the exposed, cooperative interactions between the coproporphyrin carboxylates.

Monofunctional derivatives of coproporphyrins for phosphorescent labeling of proteins and binding assays

p-Isothiocyanatophenyl derivatives of Pt(II)- and Pd(II)-coproporphyrin I are described as stable monofunctional reagents which enable simple covalent labeling of proteins and other biomolecules under mild conditions in aqueous solutions. Labeling procedure was optimized for antibodies, avidin, and neutravidin. Photophysical properties of resulting conjugates important for their use in binding assays based on time-resolved phosphorescence detection were studied. The functional activity and long-term storage stability of antibody conjugates were assessed in comparison with unmodified proteins. The new labels and their conjugates were evaluated in the solid-phase immunoassays using commercial time-resolved phosphorescence readers Victor(2) and Arcus-1230 (Wallac). Potential applications of these reagents in in vitro diagnostics are discussed.

Investigations on the formation of urinary coproporphyrin isomers I-IV in 5-aminolevulinic acid dehydratase deficiency porphyria, acute lead intoxication and after oral 5-aminolevulinic acid loading

OBJECTIVES

Investigation of the metabolism of the four urinary coproporphyrin isomers I-IV in the extremely rare 5-aminolevulinic acid dehydratase (ALAD) deficiency porphyria (syn.: Doss porphyria), in acute lead intoxication, and after oral 5-aminolevulinic acid (ALA) loading.

DESIGN AND METHODS

We analyzed the excretion of total urinary coproporphyrins and the composition of the respective isomers I-IV with ion-pair HPLC methods in these conditions.

RESULTS

The concentration of total coproporphyrins was about 30-fold increased in patients with ALAD deficiency porphyria and acute lead intoxication as compared with controls. In addition, the proportion of coproporphyrin III as well as that of the atypical isomers II and IV were significantly elevated at the expense of isomer I. After oral ALA administration to normal volunteers, a 10- to 15-fold increase in the maximal concentration of total urinary coproporphyrins was observed within 12 to 24 h. Urinary levels were back to normal after another 24 h. The excretion pattern of the individual urinary coproporphyrin isomers I-IV after ALA ingestion revealed a dynamic process: initially isomer III was preferentially formed, followed by a 3-fold increase of isomers II and IV via non-enzymatic rearrangement of isomer III, and finally normalization of all four isomers occurred within 48 h.

CONCLUSIONS

These results demonstrate that oral ALA loading can be used as an in vivo model to study the metabolism of the four urinary coproporphyrin isomers I-IV especially in ALAD deficiency porphyria and in acute lead poisoning.

Phosphorescent platinum/palladium coproporphyrins for time-resolved luminescence microscopy

Streptavidin and antibodies were labeled with phosphorescent platinum and palladium coproporphyrin. The optimal conjugates were selected on the basis of spectroscopic analysis (molar extinction coefficient, quantum yield, lifetime) and using ELISA assays to determine the retention of biological activity and immunospecificity. They were subsequently tested for the detection of prostate-specific antigen, glucagon, human androgen receptor, p53, and glutathione transferase in strongly autofluorescent tissues. Furthermore, platinum and palladium coproporphyrin-labeled dUTPs were synthesized for the enzymatic labeling of DNA probes. Porphyrin-labeled DNA probes and porphyrin-labeled streptavidin conjugates were evaluated for DNA in situ hybridization on metaphase spreads, using direct and indirect methods, respectively. The developed in situ detection technology is shown to be applicable not only in mammals but also in plants. A modular- based time-resolved microscope was constructed and used for the evaluation of porphyrin-stained samples. The time-resolved module was found suitable for detection of antigens and DNA targets in an autofluorescent environment. Higher image contrasts were generally obtained in comparison with conventional detection systems (e.g., fourfold improvement in detection of glutathione transferase).

Functional activation of antibodies on modification with Pd(II) coproporphyrin I N-Hydroxysuccinimide ester

Metalloporphyrin-antibody conjugates provide a significant advantage over other types of conjugates in biomedical use for phosphorescence immunoassay, targeted immunotherapy, and internal imaging of malignant tumors. Monoclonal HSF102 antibody of mouse IgG2a subclass and monospecific rabbit IgG, both antibodies directed to human spleen ferritin, were modified with the new reagent Pd(II) coproporphyrin I tetra-N-hydroxysuccinimide ester. Functional study of the conjugates obtained revealed a 7- and 1.4-fold increase in the antigen binding activity for monoclonal HSF102 and monospecific IgG antibodies, respectively. For rabbit monospecific IgG, a concomitant increase in binding to anti-rabbit IgG antibodies directed to the epitopes of the CH2 domain in the Fc fragment was observed. In all cases, the maximum functional activation was found after conjugating one mole porphyrin per mole antibody. These results suggest that functional activation of the conjugates might be due to an increase in conformational flexibility of an antibody molecule after the modification. This increase in flexibility involves the Fab fragments and a pair of the CH2 domains in the Fc fragment and might be due to a significant charge shift (minus 5 charge units per modified amino group) that occurs after conjugation of an antibody with tetracarboxylic porphyrin.

Spectral splitting in the alpha (Q0,0) absorption band of ferrous cytochrome c and other heme proteins

The alpha or Q0,0 absorption band of horse iron(II) cytochrome c splits and shifts to the blue as temperature decreases over the temperature range of 290-10 K. At room temperature, its maximum is at 18 150 cm-1 and the spectral width is 273 cm-1, whereas at 10 K, the two bands of the Q0,0 transition occur at 18 364 and 18 253 cm-1 and the width of the lowest-energy band is 96 cm-1. Temperature dependent splitting also occurs for zinc cytochrome c, a derivative in which Fe has been replaced by Zn; at 10 K, the peaks in the Q0,0 band region occur at 17 106 and 16 996 cm-1. The peak positions are independent of the cryosolvent (aqueous ethylene glycol or glycerol mixtures). The splitting of the Q0,0 band seen in the protein (approximately 110 cm-1 for iron and zinc cytochrome c) is comparable to the crystal field splitting observed for metalloporphyrins in mixed crystals. In contrast, the Q0,0 band of zinc coproporphyrin III in a glassy solvent (dimethylformamide/ethylene glycol) or in poly(vinyl chloride) shows a blue shift with temperature decrease but no evidence of Q0,0 splitting. Available spectral data show that the Q0,0 band is composed of two nearly degenerate electronic transitions and the split is due to the asymmetry in the heme pocket of the protein that arises from the surrounding polypeptide chain. This asymmetry results in the stabilization of one form of the excited state over the other, according to a Jahn-Teller mechanism.

Modification of monoclonal and polyclonal IgG with palladium (II) coproporphyrin I: stimulatory and inhibitory functional effects induced by two different methods

Antibodies conjugated with porphyrins and metalloporphyrins have a great potential for applications in fluorescence or phosphorescence immunoassays as well as in photodynamic therapy, radioimaging and internal radiation therapy of cancer. Here we describe how the new preactivated metalloporphyrin, palladium (II) coproporphyrin I-tetra-N-hydroxysuccinimide ester, can be covalently attached to mouse monoclonal and rabbit anti-human ferritin antibodies. The advantages of the proposed reagent over the previously reported carboxylic porphyrins coupled through carbodiimide activation are indicated. Conformational changes in antibodies caused by each of the two methods were assessed from their binding to the antigen (a probe for the antibody Fv domain) and anti-IgG antibodies probing the global conformation of the CH2 domain in the Fc fragment. Porphyrin coupling through carbodiimide activation resulted in a decrease in both functional activities of modified antibodies even at low levels of modification. In contrast, when the N-hydroxysuccinimide (NHS) derivative of porphyrin was used, enhancement of the antigen-binding affinity of porphyrin-antibody conjugates occurred due to an increase in the conformational mobility (flexibility) of the modified antibodies. The stimulatory effect of conjugation was maximal when one porphyrin molecule was coupled to an antibody molecule. Coupling of NHS-activated porphyrin at pH 7.4, 7.8 and pH 8.5 suggested that the high efficiency of the reaction at pH 8.5 could be attributed predominantly to the formation of antibody aggregates, only 50% of which were covalently cross-linked. The lowest percentage of aggregates in porphyrin-antibody conjugates was found at pH 7.4 and a molar reagent-to-protein ratio in the 10:1-40:1 range. Thus, the use of the NHS-activated carboxylic porphyrin provides a mild, simple and convenient procedure for preparing antibody conjugates with enhanced antigen-binding affinity.

Composition of urinary coproporphyrin isomers I-IV in human porphyrias

The urinary distribution and relative proportions of the four coproporphyrin isomers I-IV were investigated in 50 patients suffering from hepatic and erythropoietic types of hereditary porphyrias. A highly efficient sample preparation method was applied to isolate urinary coproporphyrins, the isomer ratios of which were quantitated by isocratic ion-pair high-performance liquid chromatography. Results showed a significant decrease (p < 0.001) of the proportion of coproporphyrin I in acute hepatic porphyria (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, porphobilinogen synthase deficiency porphyria) as compared with chronic hepatic porphyria (porphyria cutanea tarda, chronic hepatic porphyria type B and C) (13.2 +/- 5.3%, mean +/- S.D., vs. 31.4 +/- 11.5%). Conversely, the proportion of isomer III was significantly higher (p < 0.001) in acute hepatic porphyria than in chronic hepatic porphyria (80.9 +/- 5.2% vs. 62.2 +/- 10.9%). As expected, the highest level of coproporphyrin I (90.0 +/- 1.9%) was found in congenital erythropoietic porphyria. The atypical coproporphyrins II and IV were detected in all types of porphyria analysed and ranged from 0.2 to 9.0%; no significant differences were seen between acute and chronic hepatic porphyrias. The diagnostic importance of the isomer ratios of coproporphyrins I and III has been confirmed in our study, while the significance of the atypical coproporphyrin isomers II and IV is still unclear at present.

[IgG, modified with coproporphyrin I and the possibility of direct measurement of the antigen-antibody complex]

Modification of rabbit IgG by coproporphyrin I activated by Woodward's reagent K as well as antigen-binding and fluorescent properties of coproporphyrin-IgG have been studied. It was shown that coproporphyrin I modified IgG retains its capacity to bind the antigen. The formation of the immune antigen-antibody complex increases the intensity of coproporphyrin-IgG fluorescence.

Deoxyribonuclease inhibitors produced by streptomycetes

Streptomyces sp. strain No. A-5838 produces three types of inhibitors of DNase II. Two of them, DNI-2 and DNI-3, were distinguished from the previously reported DNase II inhibitors, 5838-DNI and 5923-DNI, by their inhibitory profiles towards phosphodiesterases. DNI-2 has M(r) 654, and is considered to be a coproporphyrin. DNI-3 is an acidic substance with M(r) about 60,000 as estimated by gel filtration. The inhibitory activities of both inhibitors were shown to be temperature-dependent whereas only that of DNI-2 was pH-dependent.

Isolation and characterization of zinc coproporphyrin I: a major fluorescent component in meconium

We isolated a substance from an organic extract of meconium (in neutral pH) that exhibited a porphyrin-like fluorescence peak at 580 nm on excitation at 405 nm and deduced its structure. Spectrometric data suggest that the substance is not free coproporphyrin I or free coproporphyrin III, but is a chelate of coproporphyrin I with Zn2+. We also detected a chelate of coproporphyrin III with Zn2+ by HPLC. These substances may be useful as new indicators of the presence of meconium.