Quantum control of a cat qubit with bit-flip times exceeding ten seconds

Quantum bits (qubits) are prone to several types of error as the result of uncontrolled interactions with their environment. Common strategies to correct these errors are based on architectures of qubits involving daunting hardware overheads1. One possible solution is to build qubits that are inherently protected against certain types of error, so the overhead required to correct the remaining errors is greatly reduced2-7. However, this strategy relies on one condition: any quantum manipulations of the qubit must not break the protection that has been so carefully engineered5,8. A type of qubit known as a cat qubit is encoded in the manifold of metastable states of a quantum dynamical system, and thereby acquires continuous and autonomous protection against bit-flips. Here, in a superconducting-circuit experiment, we implemented a cat qubit with bit-flip times exceeding 10 s. This is an improvement of four orders of magnitude over previously published cat-qubit implementations. We prepared and imaged quantum superposition states, and measured phase-flip times greater than 490 ns. Most importantly, we controlled the phase of these quantum superpositions without breaking the bit-flip protection. This experiment demonstrates the compatibility of quantum control and inherent bit-flip protection at an unprecedented level, showing the viability of these dynamical qubits for future quantum technologies.

New opto-electro-mechanical sensor for two-dimensions dosimetry based on radiochromic films

This work presents the validation of a new Opto‒Electro-Mechanical (MOEM) system consisting of a matrix of photodetectors for two-dimensional dosimetry evaluation with radiochromic films. The proposed system is based on a 5 × 10 matrix of photodetectors controlled by both in-house electronic circuit and graphical user interface, which enables optical measurements directly. We present the first tests performed in an X-ray machine and 137Cs source with that array by using Gafchromic EBT3 films. We obtained similar results than with a standard method (e.g. flat-bed scanner). Results were compared with Monte Carlo simulations and very good agreement was found. Results show the feasibility of using this system for dose evaluations. To the best of our knowledge, this is the first MOEM sensor for radiotherapy. Further developments are ongoing to create an advanced 16 × 16 LDRs system covering 1.6 cm × 1.6 cm with a 1 mm of spatial resolution. We point to develop a portable dosimetry tool delivering dose maps in real time to improve the clinical application of radiochromic films.

Perception of Protective Stabilization by Pediatric Dentists: A Qualitative Study

INTRODUCTION

Pediatric dentists sometimes have to care for children who refuse to cooperate with the oral examination or dental treatment. Behavior management strategies are used, such as "tell-show-do," distraction, and positive reinforcement. Anxiety management can also be performed by the use of conscious sedation (oral premedication, nitrous oxide/oxygen inhalation). Unfortunately, these techniques are sometimes insufficient for providing oral care, and protective stabilization may be an option in some situations. Little is known on the impact of physical restraint and how practitioners feel about it. The objective of this study was to evaluate the perception of dentists using protective stabilization for dental care in children.

METHODS

Semistructured qualitative interviews on the perception of pediatric dentists concerning protective stabilization were conducted in the pediatric dentistry department of the University Hospital of Toulouse, France. A thematic analysis of interview transcripts was provided via NVivo software.

RESULTS

This analysis highlighted 3 main themes. First, the perceptions of dentists concerning protective stabilization showed that this procedure has a major psychological impact and led to a feeling of professional failure. Second, the reasons for which the child was stabilized were described; these concerned the child (behavior, age, number of treatments) and the environment (the parents and the medical team). Finally, we detailed how dentists manage the effects of using of protective stabilization.

CONCLUSION

Dental surgeons must balance their requirement to make concrete decisions regarding the provision of care with their personal convictions about protective stabilization. This study also shows the need for specific training on this subject, as well as the desire of certain dentists that public authorities implement legislation on this matter.

KNOWLEDGE TRANSFER STATEMENT

The findings of this study will improve the management of young patients by identifying situations where protective stabilization may be useful (age of the child, diagnosis, protection of the child or the medical team), while showing its psychological impact on practitioners. Finally, this work provides a basis for decision makers to propose a framework for the use of physical restraint.

Cadmium bioaccumulation and gastric bioaccessibility in cacao: A field study in areas impacted by oil activities in Ecuador

Cacao from South America is especially used to produce premium quality chocolate. Although the European Food Safety Authority has not established a limit for cadmium (Cd) in chocolate raw material, recent studies demonstrate that Cd concentrations in cacao beans can reach levels higher than the legal limits for dark chocolate (0.8 mg kg^-1, effective January 1st, 2019). Despite the fact that the presence of Cd in agricultural soils is related to contamination by fertilizers, other potential sources must be considered in Ecuador. This field study was conducted to investigate Cd content in soils and cacao cultivated on Ecuadorian farms in areas impacted by oil activities. Soils, cacao leaves, and pod husks were collected from 31 farms in the northern Amazon and Pacific coastal regions exposed to oil production and refining and compared to two control areas. Human gastric bioaccessibility was determined in raw cacao beans and cacao liquor samples in order to assess potential health risks involved. Our results show that topsoils (0-20 cm) have higher Cd concentrations than deeper layers, exceeding the Ecuadorian legislation limit in 39% of the sampling sites. Cacao leaves accumulate more Cd than pod husks or beans but, nevertheless, 50% of the sampled beans have Cd contents above 0.8 mg kg^-1. Root-to-cacao transfer seems to be the main pathway of Cd uptake, which is not only regulated by physico-chemical soil properties but also agricultural practices. Additionally, natural Cd enrichment by volcanic inputs must not be neglected. Finally, Cd in cacao trees cannot be considered as a tracer of oil activities. Assuming that total Cd content and its bioaccessible fraction (up to 90%) in cacao beans and liquor is directly linked to those in chocolate, the health risk associated with Cd exposure varies from low to moderate.

Three years of antibiotic consumption evaluation in French nursing homes

OBJECTIVES

We had for aim to assess antibiotic consumption and to better understand their use in nursing homes so as to target messages on relevant practice procedures sent to prescribers.

DESIGN

The MedQual network asked nursing homes with in-house pharmacies to participate in a retrospective collection of yearly antibiotic consumption data with an Excel(®) spread sheet according to the Health Ministry recommendations.

RESULTS

Fifty-two nursing homes participated in 2011, 2012, and 74 in 2013, accounting for 10% of the Pays de la Loire region's nursing homes and 15% of beds. The medians of total antibiotic consumption in daily-defined dose for 1000 patient-days were respectively 39 (32.4-49.0), 39.3 (34.4-52.9), and 44.8 (33.6-55.4). There was no significant difference between 2011 and 2013. Penicillins (J01C) were the most commonly used class with a median of 25.7 [IQ 18.8; 33.8] in 2011 and 30.4 [IQ 23.6; 41.3] in 2013. Quinolones (J01M) were the second most commonly used class with a median of 4.6 [IQ 2.9; 5.9] in 2011 and 3.8 [IQ 2.3; 6.5] in 2013, followed by the other beta-lactams (J01D) with a median of 2.5 [IQ 1.7; 4.5] in 2011 and 2,8 [IQ 1.7; 3.8] in 2013.

CONCLUSION

The monitoring of antibiotic consumption in nursing homes in the Pays de la Loire Region since 2011 has allowed identifying inappropriate use and helped improve practices. No increase of overall consumption was observed in nursing homes but the distribution according to antibiotic class changed. The current objective is to extend this monitoring and to send personalized messages to prescribers.

A national network of infectious diseases experts

OBJECTIVES

The aim of this study was to consider the implementation of a network of infectious diseases (ID) experts to optimize the antibiotic prescriptions of community and hospital practitioners.

METHODS

An observational prospective study was conducted among ID experts in the Pays-de-la-Loire Region to evaluate the number of calls and to determine the practitioner's reasons for soliciting ID expertise. For each phone consultation, four criteria were recorded during 5 days: origin of the call (internal/external), kind of question (diagnostic/therapeutic) time spent for the advice provided, type of advice.

RESULTS

A total of 386 phone consultations for 20 infectious disease specialists were recorded during the study period (5 days); 81% were internal to the hospital, 7.7% from another hospital, and 11.3% from private practice, 56.3% of the questions concerned a therapeutic strategy, 21% a diagnostic advice, and 22.6% concerned both diagnosis and therapy. Two third of the questions were answered within 10minutes. In 68.7% of cases, the ID specialist answered immediately, 19.8% of calls required following-up the patient, 6% led to refer the patient to an ID consultation, and 5.5% to hospitalization.

CONCLUSION

The survey results stress the important need for such ID expertise, both in hospitals and in ambulatory medicine. Collaboration of ID specialists in a regional network would allow an easy and permanent access to antibiotic therapy advice for prescribers. This network would improve the quality and safety of care.

[Retrospective, descriptive, observational study of treatment of multiple actinic keratoses with topical methyl aminolevulinate and red light: results in clinical practice and correlation with fluorescence imaging]

BACKGROUND

Actinic keratosis (AK) is one of the most common skin diseases seen in clinical practice. In the last 5 years, several studies assessing the efficacy of photodynamic therapy in the treatment of multiple AKs have been published.

OBJECTIVE

We aimed to assess the clinical outcomes of photodynamic therapy in patients with multiple AKs and the correlation of those outcomes with fluorescence imaging.

MATERIAL AND METHODS

In this retrospective, descriptive, observational study of 57 patients treated in our hospital with photodynamic therapy for multiple AKs, we recorded age, sex, and lesion site (face, scalp, and dorsum of the hands). All patients were treated in the same way: methyl aminolevulinic acid (Metvix) was applied for 3 hours and the skin then irradiated with red light at 630 nm, 37 J/cm(2), for 7.5 minutes (Aktilite). The response, remission duration, tolerance, number of sessions, and fluorescence images were recorded by site. The chi(2) test was used to assess between-site differences and the correlation between fluorescence imaging and clinical response.

RESULTS

The greatest improvements were obtained for facial lesions; these required fewer sessions and remission lasted longer than lesions at other sites. The treatment was best tolerated on the dorsum of the hands. The fluorescence area and the reduction in intensity on applying treatment were found to be strongly and significantly correlated with the extent of clinical response.

CONCLUSIONS

Overall, the outcomes of treatment of multiple AKs with photodynamic therapy are better for the face than for the scalp and dorsum of the hands. Fluorescence imaging may be an effective tool for predicting response to treatment.

[Selectivity of photothermolysis in the treatment of port wine stains using multiple pulses with a pulsed dye laser]

BACKGROUND

In 25 % to 50 % of patients with port wine stains treated with pulsed dye laser (even in multiple sessions), only a partial improvement is obtained that is often unsatisfactory for the patient. Various factors have been proposed to explain the resistance to treatment, such as the presence of deep, small-caliber, or very thick vessels that cannot be coagulated with a single laser pulse. Certain mathematical models suggest that multiple pulses would be effective in coagulating those vessels without losing the selectivity of photothermolysis, since more energy could be delivered to the target structures without damaging the surrounding tissue. The aim of this study was to assess the efficacy and selectivity of photothermolysis with multiple laser pulses.

METHODS

Twelve patients with port wine stains were included in the study. Various areas of each lesion were treated with pulsed dye laser (Candela V-beam, 595 nm) using different parameters. Immediately afterwards, the treated areas were biopsied.

RESULTS

The risk of exceeding an appropriate dose was greater with small spot size, long pulse duration, short intervals between pulses, and high fluences. Heat damage was less with spots of 10 mm, short pulses, intervals of 1 minute between pulses, and low fluences. In selected cases, multiple pulses were effective and selective where single pulses did not successfully coagulate the vessels.

CONCLUSIONS

Our results indicate the enormous possibilities of multiple laser pulses for the treatment of refractory vascular lesions. In addition, we have addressed the variables defining the complex thermodynamic interaction between the laser and the cutaneous tissue and indicated the safest parameters. We discuss the possible usefulness of this approach with other lasers and skin diseases.

Biotin synthase mechanism: an overview

Biotin synthase, a member of the 'radical SAM' (S-adenosylmethionine) family, converts DTB (dethiobiotin) into biotin. The active form of the Escherichia coli enzyme contains two (Fe-S) centres, a (4Fe-4S) and a (2Fe-2S). The (4Fe-4S)2+/+ mediates the electron transfer required for the reductive cleavage of SAM into methionine and a DOA* (deoxyadenosyl radical). Two DOA*, i.e. two SAM molecules, are consumed to activate the positions 6 and 9 of DTB. A direct transfer of isotope from the labelled substrate into DOAH (deoxyadenosine) has been observed with 2H, although not quantitatively, but not with tritium. The source of the sulphur introduced to form biotin is still under debate. We have shown that the (2Fe-2S)2+ cluster can be reconstituted in the apoenzyme with S2- and Fe2+. When S2- was replaced by [34S2-], [35S2-] or Se2-, biotin containing mostly the sulphur isotopes or selenium was obtained. This leads us to favour the hypothesis that the (2Fe-2S) centre is the sulphur donor, which may explain the absence of turnover of the enzyme. DTBSH (9-mercaptodethiobiotin), which already contains the sulphur atom of biotin, was shown to be an alternative substrate of biotin synthase both in vivo and with a crude extract. When this compound was tested with a well-defined in vitro system, the same turnover of one and similar reaction rates were observed for DTB and DTBSH. We postulate that the same intermediate is formed from both substrates.

Inhibition of 7,8-diaminopelargonic acid aminotransferase by amiclenomycin and analogues

Cis and trans stereoisomers of amiclenomycin, a natural L-amino acid antibiotic, have been prepared using unequivocal routes. By using 1H NMR spectroscopy, the configuration of the six-membered ring of natural amiclenomycin was shown to be cis and not trans as originally proposed. Amiclenomycin and some synthetic analogues with the cis configuration irreversibly inactivate DAPA AT (7,8-diaminopelargonic acid aminotransferase), an enzyme involved in biotin biosynthesis, by forming an aromatic PLP (pyridoxal-5'-phosphate)-inhibitor adduct that is tightly bound to the active site. The following kinetic parameters for the inactivation of Escherichia coli DAPA AT by amiclenomycin were derived: K(I)=2 microM and k(inact)=0.4 min(-1). The structure of the aromatic adduct formed upon inactivation was confirmed by UV-visible spectroscopy, X-ray crystal structure determination and MS. Because Mycobacterium tuberculosis DAPA AT is a potential drug target, this enzyme was cloned, overexpressed and purified to homogeneity for biochemical characterization.

Enzymology of carbon-sulfur bond formation

Mobilization of the sulfur of cysteine as persulfide is the first step of sulfur transfer into thiamin, molydopterin, 4-thiouridine, biotin and lipoic acid, but then the pathways diverge completely. For the first three compounds, one or several proteinic persulfides are involved, ending in the nucleophilic attack of a sulfur, persulfide, sulfide or thiocarboxylate on a carbonyl equivalent. Several proteins have been newly characterized, revealing homologies between the three biosynthetic routes and evolutionary relationships. In the case of biotin, and very probably of lipoic acid, the sulfur is transferred as sulfide into the [Fe-S] center of the enzyme. This [Fe-S] center is the ultimate sulfur donor, which quenches a carbon radical on the substrate. This radical is produced by homolytic cleavage of a C-H bond by a deoxyadenosyl radical arising from the reduction of S-adenosylmethionine.

Biosynthesis of biotin and lipoic acid

The genetics and mechanistic enzymology of biotin biosynthesis have been the subject of much investigation in the last decade, owing to the interest for biotin production by fermentation, on the one hand, and for the design of inhibitors with potential herbicidal properties, on the other hand. Four enzymes are involved in the synthesis of biotin from its two precursors, alanine and pimeloyl-CoA. They are now well-characterized and the X-ray structures of the first three have been published. 8-Amino-7-oxopelargonic acid synthase is a pyridoxal 5'-phosphate (PLP) enzyme, very similar to other acyl-CoA alpha-oxoamine synthases, and its detailed mechanism has been determined. The origin of its specific substrate, pimeloyl-CoA, however, is not completely established. It could be produced by a modified fatty acid pathway involving a malonyl thioester as the starter. 7,8-Diaminopelargonic acid (DAPA) aminotransferase, although sharing sequence and folding homologies with other transaminases, is unique as it uses S-adenosylmethionine (AdoMet) as the NH2 donor. The mechanism of dethiobiotin synthethase is also now well understood. It catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP. On the other hand, the mechanism of the last enzyme, biotin synthase, which has long raised a very puzzling problem, is only starting to be unraveled and appears indeed to be very complex. Biotin synthase belongs to the family of AdoMet-dependent enzymes that reductively cleave AdoMet into a deoxyadenosyl radical, and it is responsible for the homolytic cleavage of C-H bonds. A first radical formed on dethiobiotin is trapped by the sulfur donor, which was found to be the iron-sulfur (Fe-S) center contained in the enzyme, and cyclization follows in a second step. Two important features come from these results: (1) a new role for an Fe-S center has been revealed, and (2) biotin synthase is not only a catalyst but also a substrate for the reaction. Lipoate synthase, which catalyzes the formation of two C-S bonds from octanoic acid, has a very high sequence similarity with biotin synthase. Although no in vitro enzymology has been carried out with lipoate synthase, the sequence homology as well as the results of in vivo studies support the conclusion that both enzymes are strongly mechanistically related.

Enzyme-mediated sulfide production for the reconstitution of [2Fe-2S] clusters into apo-biotin synthase of Escherichia coli. Sulfide transfer from cysteine to biotin

We previously showed that biotin synthase in which the (Fe-S) cluster was labelled with 34S by reconstitution donates 34S to biotin [B. Tse Sum Bui, D. Florentin, F. Fournier, O. Ploux, A. Méjean & A. Marquet (1998) FEBS Lett. 440, 226-230]. We therefore proposed that the source of sulfur was very likely the (Fe-S) centre. This depletion of sulfur from the cluster during enzymatic reaction could explain the absence of turnover of the enzyme which means that to restore a catalytic activity, the clusters have to be regenerated. In this report, we show that the NifS protein from Azotobacter vinelandii and C-DES from Synechocystis as well as rhodanese from bovine liver can mobilize the sulfur, respectively, from cysteine and thiosulfate for the formation of a [2Fe-2S] cluster in the apoprotein of Escherichia coli biotin synthase. The reconstituted enzymes were as active as the native enzyme. When [35S]cysteine was used during the reconstitution experiments in the presence of NifS, labelled (Fe35S) biotin synthase was obtained. This enzyme produced [35S]biotin, confirming the results obtained with the 34S-reconstituted enzyme. NifS was also effective in mobilizing selenium from selenocystine to produce an (Fe-Se) cluster. However, though NifS could efficiently reconstitute holobiotin synthase from the apoform, starting from cysteine, these two effectors had no significant effect on the turnover of the enzyme in the in vitro assay.

Differential protein kinase C phosphorylation sites in the L17 ribosomal protein from Leishmania infantum

Leishmania infantum, the protozoan parasite responsible for leishmaniasis in Europe, is capable of undergoing developmental changes in vitro and provides an excellent model for the study of cell differentiation processes. We have cloned the gene encoding the L17 ribosomal protein. The LiL17 protein family belongs to the macrolide binding site, related to the peptidyl transferase center of the ribosome. Its comparison with other members of the protein family shows several structural differences that may reflect functional variations. The protein kinase C phosphorylation sites display an intermediate pattern involving differences in location and type of residue with respect to all the species considered. Gene-structural analysis suggests the existence of two different encoding genes. The expression of the genes seem to be different with the distinct growth phases of the parasite.

Mössbauer studies of Escherichia coli biotin synthase: evidence for reversible interconversion between [2Fe-2S](2+) and [4Fe-4S](2+) clusters

The nature and properties of the iron-sulphur (Fe-S) cluster in as-prepared and reduced biotin synthase of Escherichia coli have been investigated by Mössbauer spectroscopy. Our data clearly demonstrate that in the as-prepared sample, the cluster is present as [2Fe-2S](2+) with isomer shift, delta = 0.29 mm/s and quadrupole splitting, DeltaE(Q) = 0.53 mm/s, indicating incomplete cysteinyl-S coordination. Anaerobic reduction by dithionite in the presence of 55% (v/v) glycerol converts this form to [4Fe-4S](2+) (delta = 0.45 mm/s and DeltaE(Q) = 1.11 mm/s) and is accompanied by some destruction to Fe(2+). This cluster conversion is reversible and when exposed to air, the [4Fe-4S](2+) cluster is quantitatively reconverted to the [2Fe-2S](2+) cluster without any further cluster degradation.

Molecular cloning, cell localization and binding affinity to DNA replication proteins of the p36/LACK protective antigen from Leishmania infantum

The p36/LACK antigen from Leishmania, an analogue of the receptor for activated protein kinase C (PKC), induces high levels of protection against parasite infection in the BALB/c mouse model. This protection is more than twice as high as that elicited by major parasite antigens such as soluble Leishmania antigen or the main surface protease gp63. We have cloned and purified p36/LACK from Leishmania infantum, the causative agent of visceral leishmaniasis in Europe. This protein belongs to the large family of WD 40 repeat proteins confined to eukaryotes and involved in numerous regulatory functions. Differential solubilization and immunofluorescence experiments indicate that p36/LACK is present close to the kinetoplast disc in the cell cytoplasm, probably bound to multiprotein complexes but not to membrane structures. These complexes probably also include cytoplasm PKC isoforms. The use of a genetically-encoded peptide library indicates that p36/LACK binds sequences present in several proteins involved in DNA replication and RNA synthesis. The recognition and binding sequences present in vacuolar proteins and at the beta-chain of major histocompatability complex (MHC) class II suggest the involvement of this regulatory protein in the early mechanisms triggering the protective immune response of the host against the parasite infection.

Cloning, molecular analysis and differential cell localisation of the p36 RACK analogue antigen from the parasite protozoon Crithidia fasciculata

The family of the RACK molecules (receptors for activated C kinases) are present in all the species studied so far. In the genus Leishmania, these molecules also induce a strong immune reaction against the infection. We have cloned and characterised the gene that encodes the RACK analogue from the parasite trypanosomatid Crithidia fasciculata (CACK). The molecule seems to be encoded by two genes. The sequence analysis of the cloned open reading frame indicates the existence of a high degree of conservation not only with other members of the Trypanosomatidae but also with mammalians. The study of the protein kinase C phosphorylation sites shows the presence of three of them, shared with the mammalian species, additional to those present in the other protozoa suggesting a certain phylogenetic distance between the protozoon Crithidia fasciculata and the rest of the Trypanosomatidae. The CACK-encoded polypeptide shows an additional sequence of four amino acids at the carboxy-terminal end, which produces a different folding of the fragment with the presence of an alpha-helix instead of the beta-sheet usual in all the other species studied. A similar result is elicited at the amino-terminal end by the change of three amino acid residues. The immunolocalisation experiments show that the CACK displays a pattern with a distribution mainly at the plasma membrane, different from that of the related Leishmania species used as control, that displays a distribution close to the nucleus. Altogether, the data suggest that the existence of the structural differences found may have functional consequences.

Slow-binding and competitive inhibition of 8-amino-7-oxopelargonate synthase, a pyridoxal-5'-phosphate-dependent enzyme involved in biotin biosynthesis, by substrate and intermediate analogs. Kinetic and binding studies

8-Amino-7-oxopelargonate synthase catalyzes the first committed step of biotin biosynthesis in micro-organisms and plants. Because inhibitors of this pathway might lead to antibacterials or herbicides, we have undertaken an inhibition study on 8-amino-7-oxopelargonate synthase using six different compounds. d-Alanine, the enantiomer of the substrate of this pyridoxal-5'-phosphate-dependent enzyme was found to be a competitive inhibitor with respect to l-alanine with a Ki of 0.59 mm. The fact that this inhibition constant was four times lower than the Km for l-alanine was interpreted as the consequence of the inversion-retention stereochemistry of the catalyzed reaction. Schiff base formation between l or d-alanine and pyridoxal-5'-phosphate, in the active site of the enzyme, was studied using ultraviolet/visible spectroscopy. It was found that l and d-alanine form an external aldimine with equilibrium constants K = 4.1 mm and K = 37.8 mm, respectively. However, the equilibrium constant for d-alanine aldimine formation dramatically decreased to 1.3 mm in the presence of saturating concentration of pimeloyl-CoA, the second substrate. This result strongly suggests that the binding of pimeloyl-CoA induces a conformational change in the active site, and we propose that this new topology is complementary to d-alanine and to the putative reaction intermediate since they both have the same configuration. (+/-)-8-Amino-7-oxo-8-phosphonononaoic acid (1), the phosphonate derivative of the intermediate formed during the reaction, was our most potent inhibitor with a Ki of 7 microm. This compound behaved as a reversible slow-binding inhibitor, competitive with respect to l-alanine. Kinetic investigation showed that this slow process was best described by a one-step mechanism (mechanism A) with the following rate constants: k1 = 0.27 x 103 m-1.s-1, k2 = 1.8 s-1 and half-life for dissociation t1/2 = 6.3 min. The binding of compound 1 to the enzyme was also studied using ultraviolet/visible spectroscopy, and the data were consistent with the kinetic data (K = 4.2 microm). Among the other compounds tested, two potential transition state analogs, 4-carboxybutyl(1-amino-1-carboxyethyl)phosphonate (4) and 2-amino-3-hydroxy-2-methylnonadioic acid (5) were found to be competitive inhibitors with respect to l-alanine with Ki of 68 microm and 80 microm, respectively.

Biotin synthase mechanism: on the origin of sulphur

Biotin synthase catalyses the last step of the biosynthesis of biotin in microorganisms and plants. The active protein isolated from Bacillus sphaericus and Escherichia coli contains an iron-sulphur (FeS) cluster. The native enzymes were depleted of their iron and inorganic sulphide and the resulting apoenzymes were chemically reconstituted with FeCl3 and Na2[34S] to give labelled (Fe34S) enzymes. These enzymes were functional and when assayed in vitro produced labelled biotin containing about 65% of 34S. These data strongly support the hypothesis that the sulphur of biotin is derived from the (FeS) centre of the enzyme.

Photoaffinity labelling of the human mineralocorticoid receptor with steroids having a reactive group at position 3, 18 or 21

The ability of a glucocorticoid (triamcinolone acetonide: TA) and three progesterone derivatives with photoreactive groups at different positions (promegestone: R5020; 18-oxo-18-vinylprogesterone: 18OVP; 21-diazoprogesterone: 21DP) to bind covalently to the human mineralocorticoid receptor (hMR) expressed in Sf9 insect cells was assessed. Sedimentation gradient analysis and exchange assays with aldosterone showed that [3H]TA, a partial mineralocorticoid agonist, and [3H]R5020, a pure antimineralocorticoid, were covalently bound to hMR after UV irradiation, with a labelling efficiency of approx. 3-5%. UV irradiation did not alter the heterooligomeric structure of the hMR, since the irradiated [3H]TA- and [3H]R5020-hMR complexes sedimented at approx. 9-10 S, as did the non-irradiated complexes. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed a band labelled by [3H]TA or [3H]R5020, having a molecular mass of 120 kDa. This band was not detected in the presence of an excess of the corresponding unlabelled steroid or when the cytosol was recovered from non-infected Sf9 cells. Electrophoresis of a truncated hMR (hMRDelta(1-351)) photolabelled with [3H]TA revealed a 80 kDa band, compatible with the molecular mass of the truncated hMR. Limited chymotrypsin proteolysis of the [3H]TA photolabelled hMR generated a 30 kDa fragment covalently associated with [3H]TA. As the 30 kDa fragment generated by chymotrypsin has been shown to encompass the entire ligand-binding domain of the hMR (B. Couette, J. Fagart, S. Jalaguier, M. Lombès, A. Souque, M.E. Rafestin-Oblin, Biochem. J. 315 (1996) 421-427), the present experiments provide evidence that [3H]TA is covalently bound to the ligand binding domain of the hMR. Exchange assays with [3H]A also revealed that unlabelled 18OVP and 21DP, two mineralocorticoid agonists bearing photoreactive groups at skeleton positions crucial for the ligand-MR interaction, are covalently bound to hMR with an approx. 30-35% labelling efficiency.

18-Vinyldeoxycorticosterone: a potent inhibitor of the bovine cytochrome P-450(11) beta

18-Vinylprogesterone (18-VP) and 18-ethynylprogesterone (18-EP) have proved to be potent suicide inhibitors of P-450(11) beta, the last enzyme of aldosterone biosynthesis (Delorme, C.; Piffeteau, A.; Viger, A.; Marquet, A. Eur. J. Biochem. 1995, 232, 247; Delorme, C.; Piffeteau, A.; Sobrio, F.; Marquet, A. Eur. J. Biochem. 1997, 248, 252). This paper describes the synthesis of 18-vinyldeoxycorticosterone (18-VDOC), an analogue of deoxycorticosterone (DOC), the physiological substrate of the enzyme, and the evaluation of its reversible inhibiting properties for deoxycorticosterone and corticosterone oxidation by the bovine enzyme. 18-VDOC has been obtained by hydroxylation at C-21 of a 18-VP precursor. Its reversible Ki values are, respectively, 0.3 microM for the 11 beta-hydroxylation and 0.8 microM for the 18-hydroxylation. Hence, 18-VDOC is the strongest competitive inhibitor of bovine P-450(11) beta described so far, but in contrast with 18-VP, it does not inhibit more efficiently the 18-hydroxylation than the 11-hydroxylation.

Cloning and structural analysis of the gene encoding the ribosomal protein S6 from the parasite Leishmania infantum

We have cloned the S6 ribosomal protein encoding gene from a Leishmania infantum cDNA library. This parasite protozoon, responsible for leishmaniasis in Europe, is able to undergo developmental changes in vitro and results a good model to study cell differentiation processes. The LiS6 protein sequence indicates its pertinence to the S6 protein family, related to the early mechanisms of cell division, differentiation and activation, and shows an intermediate position between the yeasts and higher eukaryotes. Thus, LiS6 protein has the same amino acid length as that of the higher eukaryotes and certain common features such nucleus entrance sequences and several kinase phosphorylation sites. However, the key functional protein kinase C phosphorylation sites are at different locations and present several threonine instead of the usual serine residues. The gene structural analysis suggest the presence of three different encoding genes that do not present remarkable changes along the different phases of the parasite.

Mechanism-based inactivation of bovine cytochrome P-450(11beta) by 18-unsaturated progesterone derivatives

Two 18-unsaturated progesterone derivatives, 18-vinylprogesterone (18-VP) and 18-ethynylprogesterone (18-EP) have proved to be potent inhibitors of the bovine cytochrome P-450(11beta), the enzyme involved in the last steps of aldosterone biosynthesis [Delorme, C., Piffeteau, A., Viger, A. & Marquet, A. (1995) Eur. J. Biochem. 232, 247-256]. In the present study, we demonstrate that these two compounds exhibit the characteristics of mechanism-based inactivators of this enzyme. Inactivation followed pseudo-first-order and saturation kinetics. The kinetic parameters of inactivation were k(i) = 0.11 min(-1) and Ki = 4 microM for 18-VP, and k(i) = 0.12 min(-1) and 22 microM for 18-EP. Inactivation of P-450(11beta) activity was strictly dependent on the presence of NADPH. Protection by the substrate deoxycorticosterone was observed, demonstrating a selective modification at the substrate-binding site. With radiolabeled 18-VP, inactivation was shown to be irreversible with a stoichiometry of 1.4 mol bound [3H]18-VP/mol inactivated cytochrome P-450(11beta). SDS/PAGE analysis of the [3H]18-VP-inactivated enzyme showed that, under conditions preventing heme dissociation, the P-450(11beta) band was labeled, while no labeling of the apoprotein was observed under denaturating conditions. Furthermore, the loss of catalytic activity could be correlated with the destruction of the P-450 chromophore evaluated by the FeII-CO versus FeII difference spectra. These arguments led us to propose that 18-vinylprogesterone inactivates cytochrome P-450(11beta) by heme destruction rather than by protein modification.

The active site region of the vitamin K-dependent carboxylase includes both the amino-terminal hydrophobic and carboxy-terminal hydrophilic domains of the protein

In order to localize the active site of the vitamin K-dependent carboxylase, we developed an affinity probe containing the propeptide and the first two carboxylatable glutamate residues conserved in many native substrates. This probe crosslinked to both the hydrophobic amino-terminal and hydrophilic carboxy-terminal domains of the carboxylase, in contrast with previous work which localized both the catalytic and the propeptide binding site within the amino-terminal hydrophobic domain. Amino acid analysis revealed that the mass of an amino-terminal fragment is seriously underestimated by SDS-PAGE. Reanalysis of the published data in light of this information suggests that a portion of the propeptide binding site resides within the carboxy-terminal hydrophilic domain.

Biotin synthase, a new member of the family of enzymes which uses S-adenosylmethionine as a source of deoxyadenosyl radical

The fact that biotin synthase, from Escherichia coli and Bacillus sphaericus, requires S-adenosylmethionine and a reducing system led us to postulate that this synthase could belong to the family of enzymes which use S-adenosylmethionine as a source of deoxyadenosyl radical, namely pyruvate formate-lyase, lysine 2,3-aminomutase, and anaerobic ribonucleotide reductase. We describe here experiments with S-[2,8-(3)H] adenosylmethionine and S-adenosyl-[methyl-3H]methionine which allowed the identification and quantification of the expected cleavage products, deoxyadenosine, and methionine. They are formed in equimolar amounts, in a ratio close to 3 with respect to the biotin produced. We postulate a mechanism involving the homolytic cleavage of two C-H bonds which should consume two equivalents of S-adenosylmethionine. The observed excess of S-adenosylmethionine consumption is attributed to abortive processes.

Cloning of the gp63 surface protease of Leishmania infantum. Differential post-translational modifications correlated with different infective forms

The Leishmania cell surface virulence factor gp63 is a protease family that plays an important role in the survival of the parasite protozoon into the host macrophages. We have cloned and characterised the gp63 gene from L. infantum. The sequence analysis of the gene indicates the existence of a high degree of conservation with the other old world species L. major and L. donovani. The similarity is lower with new world species with the exception of L. chagasi which shows a strikingly high percentage of identity (99-100%). In L. infantum the gp63 gene expresses two polypeptides of 58 and 60 kDa, respectively, which show a similar proteolytic activity. The 60 kDa polypeptide is expressed during the whole life cycle of the promastigote form of the parasite with a moderate increase at the stationary phase of growth while the 58 kDa product, although slightly present in the logarithmic phase, notable increases its expression during the highly infectious stationary phase. RNA analysis showed that the presence in L. chagasi of these two polypeptides correlates with two RNA molecules and with the degree of parasite infectivity, whereas in the case of L. infantum a single 3 kb messenger RNA is detected through the whole promastigote life cycle. Our data indicate that in L. infantum, the differences in gene expression of the gp63 protease family according to parasite phase of growth seem to be due to a differential pattern of glycosilation of the polypeptides which correlates with the different infective forms of the promastigote form of the parasite.

New steroidal diazo ketones as potential photoaffinity labeling reagents for the mineralocorticoid receptor: synthesis and biological activities

Three diazo ketones in the progesterone series were synthesized as potential photoaffinity reagents. The diazo ketone group was introduced at the C17 (21-diazopregn-4-ene-3,20-dione, 1) or C13 (18-(diazomethyl)-20-hydroxypregn-4-ene-3,18-dione, 2, 18-(diazomethyl)pregn-4-ene-3, 18,20-trione, 3) position of the pregnene skeleton. Whereas compound 1 could be easily obtained from the corresponding acid chloride, preparation of 2 and 3 required a less straightforward route involving reaction of tosyl azide on the formyl derivative of methyl ketone 5. The affinity of the diazo ketones for the human mineralocorticoid receptor (hMR), expressed in Sf9 insect cells using the Baculovirus system, was estimated by competition experiments using [3H]aldosterone as specific ligand. The affinity of 1 for hMR was almost identical with that of aldosterone. The affinities of 2 and 3 were 1, order of magnitude lower than that of aldosterone. The mineralocorticoid activity of the diazo ketones was measured in cis-trans cotransfection assays in CV-1 cells with the mouse mammary tumor virus as DNA target sequence. Compound 1 exhibits an agonist activity (ED50 = 6 x 10(-9) M) with no antagonist activity. In contrast 2 and 3 behave as antagonists, displaying an IC50 of approximately 10(-6) M whether the substituent at the C20 position is a hydroxy (2) or an oxo (3) group.