Mechanism and dynamics of fatty acid photodecarboxylase

Fatty acid photodecarboxylase (FAP) is a photoenzyme with potential green chemistry applications. By combining static, time-resolved, and cryotrapping spectroscopy and crystallography as well as computation, we characterized Chlorella variabilis FAP reaction intermediates on time scales from subpicoseconds to milliseconds. High-resolution crystal structures from synchrotron and free electron laser x-ray sources highlighted an unusual bent shape of the oxidized flavin chromophore. We demonstrate that decarboxylation occurs directly upon reduction of the excited flavin by the fatty acid substrate. Along with flavin reoxidation by the alkyl radical intermediate, a major fraction of the cleaved carbon dioxide unexpectedly transformed in 100 nanoseconds, most likely into bicarbonate. This reaction is orders of magnitude faster than in solution. Two strictly conserved residues, R451 and C432, are essential for substrate stabilization and functional charge transfer.

Using X-rays in photodynamic therapy: an overview

Photodynamic therapy is a therapeutic option to treat cancer and other diseases.

Structure of cytochrome c7 from Desulfuromonas acetoxidans at 1.9 A resolution

Multihaem cytochromes play a key role in electron-transport reactions in the periplasm of sulfate- and sulfur-reducing bacteria. The redox proteins grouped in the c3 superfamily also display metal-reducing activities, which make them interesting biotechnological tools. The crystal structure of the fully oxidized cytochrome c7 from Desulfuromonas acetoxidans has been solved by combined molecular-replacement and MAD methods. The structure has been refined at 1.9 A resolution to an R value of 19.1% (R(free) = 24.3%) and includes three haems and 116 water molecules. The protein displays the cytochrome c3 fold in a highly minimized form, while haem 2 and the surrounding protein environment are missing. The geometry of haem packing and of the haem axial ligands and propionates are described and compared with that of c3 cytochromes. The crystal structure is compared with the solution structure recently obtained by NMR methods and with its homologue cytochromes of the c3 superfamily. Comparison of the high number of available structures makes it possible to analyze the structural role of the few highly conserved residues, in addition to the cysteines and histidines that link the porphyrin rings and the Fe atoms to the protein chain.

Functional aspects of the heme bound hemophore HasA by structural analysis of various crystal forms

The protein HasA from the Gram negative bacteria Serratia marcescens is the first hemophore to be described at the molecular level. It participates to the shuttling of heme from hemoglobin to the outer membrane receptor HasR, which in turn releases it into the bacterium. HasR alone is also able to take up heme from hemoglobin but synergy with HasA increases the efficiency of the system by a factor of about 100. This iron acquisition system allows the bacteria to survive with hemoglobin as the sole iron source. Here we report the structures of a new crystal form of HasA diffracting up to 1.77A resolution as well as the refined structure of the trigonal crystal form diffracting to 3.2A resolution. The crystal structure of HasA at high resolution shows two possible orientations of the heme within the heme-binding pocket, which probably are functionally involved in the heme-iron acquisition process. The detailed analysis of the three known structures reveals the molecular basis regulating the relative affinity of the heme/hemophore complex.

The crystal structure of HasA, a hemophore secreted by Serratia marcescens

Free iron availability is strongly limited in vertebrate hosts, making the iron acquisition by siderophores inappropriate. Pathogenic bacteria have developed various ways to use the host's iron from iron-containing proteins. Serratia marcescens can use the iron from hemoglobin through the secretion of a hemophore called HasA, which takes up the heme from hemoglobin and shuttles it to the receptor HasR, which in turn, releases heme into the bacterium. We report here the first crystal structure of such a hemophore, bound to a heme group at two different pH values and at a resolution of 1.9 A. The structure reveals a new original fold and suggests a hypothetical mechanism for both heme uptake and release.

Key role of phenylalanine 20 in cytochrome c3: structure, stability, and function studies

Aromatic residues in c-type cytochromes might have an important function in the folding and/or electron transferring properties of the molecule. In the tetraheme cytochrome c3 (Mr 13 000) from Desulfovibrio vulgaris Hildenborough, Phe20, is located between heme 1 and heme 3 with its aromatic ring close and almost parallel to the ring plane of heme 1. We replaced this residue by a nonaromatic hydrophobe residue, leucine, and analyzed the effects in terms of functional, structural, and physicochemical properties. While the F20L replacement did not have any strong effects on the heme region stability, a decrease of the thermostability of the whole molecule was observed. In the same way, the four macroscopic redox potentials were affected by the mutation as well as the flexibility of the surface loop around heme 4. The F20L replacement itself and/or this structural modification might be responsible for the loss of the intermolecular cooperativity between F20L cytochrome c3 molecules.

Drug analysis of biological samples. A survey of validation approaches in chromatography in the UK pharmaceutical industry

1. The results of a survey on validation of analytical chromatographic methods are reported. The survey was carried out in 1990 within most of the principal British Pharmaceutical Companies. 2. A general method of validation is established from the collated results. 3. A comparison is made with existing reports from international meetings.

Quantitative high-performance liquid chromatographic, gas chromatographic, and gas chromatographic-mass spectrometric analysis of ticlopidine in baboon plasma after solid-phase extraction

High-performance liquid chromatography with UV detection (HPLC-UV) and gas chromatography with either nitrogen phosphorus (GC-NPD) or mass spectrometry (GC-MS) detection were used for the determination of ticlopidine in plasma. Solid-phase extraction of ticlopidine from plasma was performed using Extrelut columns without pH adjustment, and using hexane as the solvent of elution. With HPLC, a mobile phase of 0.01 M pH 7.8 phosphate buffer:acetonitrile (70:30) was passed through a mu Bondapack C-18 column at a rate of 1.3 mL/min. Ultraviolet detection at 235 nm was sensitive to plasma ticlopidine concentrations of 0.05 micrograms/mL. The GC-NPD and GC-MS were performed on a DB-17 fused-silica column using on-column injection. For GC-NPD and GC-MS, limits of quantification were found to be 0.020 and 0.005 micrograms/mL, respectively. Compared with HPLC-UV, the GC methods were found to be more reproducible, sensitive, and specific and therefore more suitable for pharmacokinetic applications.

Direct determination of mitoxantrone and its mono- and dicarboxylic metabolites in plasma and urine by high-performance liquid chromatography

The simultaneous isolation and determination of mitoxantrone (Novantrone) and its two known metabolites (the mono- and dicarboxylic metabolites) were carried out using a high-performance liquid chromatographic (HPLC) system equipped with an automatic pre-column-switching system that permits drug analysis by direct injection of biological samples. Plasma or urine samples were injected directly on to an enrichment pre-column flushed with methanol-water (5:95, v/v) as the mobile phase. The maximum amount of endogenous water-soluble components was removed from biological samples within 9 min. Drugs specifically adsorbed on the pre-column were back-flushed on to an analytical column (Nucleosil C18, 250 X 4.6 mm I.D.) with 1.6 M ammonium formate buffer (pH 4.0) (2.5% formic acid) containing 20% acetonitrile. Detection was effected at 655 nm. Chromatographic analysis was performed within 12 min. The detection limit of the method was about 4 ng/ml for urine and 10 ng/ml for plasma samples. The precision ranged from 3 to 11% depending on the amount of compound studied. This technique was applied to the monitoring of mitoxantrone in plasma and to the quantification of the unchanged compound and its two metabolites in urine from patients receiving 14 mg/m2 of mitoxantrone by intravenous infusion for 10 min.

Simultaneous determination of tropatepine and its major metabolites by high-performance liquid chromatographic-mass spectrometric identification. Application to metabolic and kinetic studies

Tropatepine is used to combat against extrapyramidal syndrome induced by neuroleptic drugs. A high-performance liquid chromatographic method was proposed for the simultaneous determination of tropatepine and its potential metabolites in biological fluids. After double extraction of compounds in hexane and back-extraction in hydrochloric acid, the chromatographic separation was performed on a reversed-phase column with an acetonitrile--perchlorate buffer mixture as mobile phase. Compounds were detected at 229 nm and the detection limit was about 15 ng/ml. The method was applied to bile and urine samples collected in rats, after a single high oral dose of 100 mg/kg of tropatepine hydrochloride. Gas chromatography-mass spectrometry was used for identification of the potential metabolites. Nortropatepine and tropatepine S-oxide were identified in this way, and it seemed that tropatepine was subjected to a large and intense metabolic process. The analytical procedure and the results of the metabolic investigation were applied to a preliminary pharmacokinetic study in patients undergoing long-term oral therapy with tropatepine.