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F Bouvier

Publications and source records attributed to F Bouvier.

At least 37 records · Page 2Linked to original sources
PubMed1998

Xanthophyll biosynthesis: molecular and functional characterization of carotenoid hydroxylases from pepper fruits (Capsicum annuum L.).

To dissect the mechanism by which carotenoid hydroxylases catalyze xanthophyll formation, we have cloned two pepper cDNAs encoding beta-cryptoxanthin and zeaxanthin biosynthetic enzymes. Using an in vitro system, we find that both enzymes are ferredoxin dependent and that their activity is strongly inhibited by iron chelators such as o-phenanthroline or 8-hydroxyquinoline. This suggests the transfer of a reducing equivalent from NADPH to the hydroxylase via ferredoxin and the involvement of an iron activated oxygen insertion process. Based on sequence analysis, the putative histidine clusters involved in the iron coordination were identified and their roles evaluated. Following site-directed mutagenesis of the identified histidine residues hydroxylase activity was totally inactivated. Collectively, our data indicate that carotenoid hydroxylases belong to a new class of diiron proteins structurally related to membrane fatty acid desaturases. Mechanistically, both types of enzymes exploit iron activated oxygen to break the C-H bond with concomitant formation of double bond or oxygen insertion. We propose that the same mechanism operates for beta-carotene ketolase and probably for other carotenoid oxygenases as well.

Amino Acid Sequence↗
PubMed1998

Comparison of different echocardiographic methods with radionuclide imaging for measuring left ventricular ejection fraction during acute myocardial infarction treated by thrombolytic therapy.

The aim of this study was to: (1) compare the usefulness, in clinical practice, of different echocardiographic methods of left ventricular (LV) function determination in patients with a recent thrombolytic-treated acute myocardial infarction (AMI); (2) compare these measurements with the reference method radionuclide imaging; and (3) evaluate the reproducibility of visual estimation of the LV ejection fraction (EF) and the use of the biplane method of discs (Simpson's rule) in clinical practice. Echocardiography and radionuclide imaging were performed within 2 hours of each another, 5 to 8 days after hospital admission. Ninety-six patients (70 men and 26 women) age 64 +/- 9 years (range 45 to 75) were studied. The echocardiographic study was performed by 2 experienced physicians, independently of each another. LV wall motion score index and visual estimation of the EF correlated best with the radionuclide EF (r = 0.72 and r = 0.71), thereafter simply counting the number of affected LV segments (r = 0.67) or atrioventricular plane measurements (r = 0.64). Simpson's rule had low correlation to the radionuclide EF (r = 0.45 to 0.51) and could not be used in approximately half of the patients due to poor identification of endocardial borders. The interobserver coefficient of variation for independent visual echocardiographic estimation of the EF was 10%, for Simpson's rule 18%, and for the radionuclide EF 5%. We conclude that the EF estimated from quantitative echocardiographic volume calculations (Simpson's rule) may differ substantially from radionuclide methods of measuring the EF. However, with experienced sonographers, the LV wall motion score index or visual estimation of the EF had reasonable agreement with the radionuclide EF in most of the patients. Atrioventricular plane measurement is an acceptable alternative.

Aged↗
PubMed1998

Metabolic compartmentation of plastid prenyllipid biosynthesis--evidence for the involvement of a multifunctional geranylgeranyl reductase.

The addition of phytyl side chain to chlorophylls, tocopherols and phylloquinone is prerequisite to their integration into plastid membranes. We have cloned a cDNA encoding a pre-geranylgeranyl reductase from Arabidopsis thaliana. The deduced primary structure predicts a mature size with a molecular mass of 47 kDa and displays a characteristic dinucleotide binding domain. Geranylgeranyl reductase expressed in Escherichia coli sequentially catalyzes the reduction of geranylgeranyl-chlorophyll a into phytyl-chlorophyll a as well as the reduction of free geranylgeranyl diphosphate into phytyl diphosphate. Due to its multifunctionality and weak hydrophobicity, we suggest that in plastid the same geranylgeranyl reductase is recruited into the chlorophyll, the tocopherol and the phylloquinone pathways. The geranylgeranyl reductase gene is up-regulated during etioplast to chloroplast and chloroplast to chromoplast development.

Amino Acid Sequence↗
PubMed1998

Left ventricular function in endurance runners during exercise.

Left ventricular function in elite runners and controls was compared by means of nuclear angiocardiography. Fifteen middle- or long-distance runners and a control group of 10 sedentary to moderately physically active subjects were studied at rest and during semi-sitting incremental exercise. Ejection fraction was higher in the runners than the controls both at rest and during exercise. At the transition from rest to exercise left ventricular end-diastolic volume initially increased similarly in runners and controls by an average of 14 and 12%, respectively, with an increase in stroke volume by approximately 25 and 23%. The parallel increase in stroke volume and left ventricular end-diastolic volume could at least partly be because of the Frank-Starling mechanism. With increasing workloads, left ventricular end-diastolic volume and ejection fraction remained fairly constant, resulting in an unchanged stroke volume from the lowest to the highest exercise intensity. This was in the runners accomplished by a 41% increase in peak filling rate and a 38% increase in peak emptying rate with similar changes observed in the controls. This has to be due to increased myocardial contractility paralleling the systolic shortening with increasing heart rate. We conclude that endurance-trained athletes have a better systolic function expressed as higher ejection fraction both at rest and during exercise than untrained subjects reflecting an enhanced myocardial contractility contributing to the maintenance of a large stroke volume during exercise. The regulatory mechanisms however, appear to be similar for athletes and healthy controls.

Adult↗
PubMed1998

Myocardial perfusion scintigraphy (SPECT) during adenosine stress can be performed safely early on after thrombolytic therapy in acute myocardial infarction.

The objective of this study was to evaluate the safety of myocardial perfusion scintigraphy with Tc-99 m sestamibi during adenosine stress in patients with recent thrombolytically treated myocardial infarction. Eighty-four patients with thrombolytically treated myocardial infarction, 59 males and 25 females, aged 62.9 +/- 8.4, were eligible for myocardial perfusion scintigraphy during adenosine provocation. Exclusion criteria for adenosine stress were hypotension, unstable angina pectoris, cardiac failure, pericarditis and atrioventricular block (AV block) II-III. Adenosine-stress and resting myocardial perfusion scintigraphy was performed 2-5 days after thrombolysis. Scintigraphy at rest was done 24 h after the stress study. Sixty patients (71%) experienced some kind of side-effects during adenosine infusion. The most frequent side-effects were dyspnoea in 43/84 patients (51%) and unspecific chest discomfort in 26/84 patients (31%). During infusion, ST depressions or elevations on ECG were seen in 9 patients (11%), 5 of whom experienced atypical chest discomfort. Five patients (6%) described typical angina but none of them showed electrographic signs of myocardial ischaemia during infusion. Six patients (7%) developed transient AV block I-II. Reversible scintigraphic perfusion defects were seen in 67 patients (79%). No serious complications, such as death, reinfarction or severe arrhythmias, occurred during adenosine infusion or during a 3-day clinical follow-up period. In conclusion, MIBI-SPECT during adenosine stress is a safe diagnostic method that can be performed in most patients early on after thrombolytically treated acute myocardial infarction. Side-effects are common but benign, and not different from those seen in patients with chronic coronary artery disease.

Adenosine↗
PubMed1998

Functional integration of non-native carotenoids into chloroplasts by viral-derived expression of capsanthin-capsorubin synthase in Nicotiana benthamiana.

The biosynthesis of leaf carotenoids in Nicotiana benthamiana was altered by forced re-routing of the pathway to the synthesis of capsanthin, a non-native chromoplast-specific xanthophyll, using an RNA viral vector containing capsanthin-capsorubin synthase (Ccs) cDNA. The cDNA encoding Ccs was placed under the transcriptional control of a tobamovirus subgenomic promoter. Leaves from transfected plants expressing Ccs developed an orange phenotype and accumulated high levels of capsanthin (up to 36% of total carotenoids). This phenomenon was associated with thylakoid membrane distortion and reduction of grana stacking. In contrast to the situation prevailing in chromoplasts, capsanthin was not esterified and its increased level was balanced by a concomitant decrease of the major leaf xanthophylls, suggesting an autoregulatory control of chloroplast carotenoid composition. Capsanthin was exclusively recruited into the trimeric and monomeric light-harvesting complexes of photosystem II (PSII) and shown to significantly contribute to the light-harvesting capacity. On a chlorophyll basis, the concentrations of PSI and PSII reaction centres were not modified. This demonstration that higher plant antenna complexes can accommodate non-native carotenoids provides compelling evidence for functional remodelling of photosynthetic membranes toward a better photoreactivity by rational design of the incorporated carotenoid structures.

Amino Acid Sequence↗
PubMed1998

Delayed recovery of myocardial perfusion in acute myocardial infarction: a scintigraphic study after early thrombolytic treatment.

BACKGROUND: Assessments of compromised myocardium and infarct size early after thrombolytic treatment in acute myocardial infarction (AMI) are important for risk stratification and for treatment management. We have therefore evaluated the clinical usefulness of myocardial perfusion scintigraphy (MIBI-SPECT) for the assessment of myocardial viability early after AMI. METHODS: Seventy-one patients [53 men and 18 women, aged 64 +/- 9 years (range 45-75 years)] with AMI treated by thrombolysis took part in this prospective study at University Hospital, Stockholm, Sweden. Sixty of them underwent adenosine-stress and resting MIBI-SPECT 2-4 days after AMI, and 11 were examined only at rest. Six months after the AMI, a repeat MIBI-SPECT at rest was obtained for comparison. RESULTS: All patients had significant perfusion defects compared with an age- and sex-matched healthy reference population. Seventy-six percent of the patients able to undergo a complete adenosine-stress and rest SPECT showed signs of reversible perfusion defects. Defect size (extent) and severity at rest decreased between the tests at 2-5 days and 6 months after AMI (P < 0.001). Reversible perfusion defects early after AMI were not related to spontaneous improvement of myocardial perfusion 6 months later. Early, semiquantitative MIBI-SPECT was not able to predict final infarct size as measured by resting perfusion data 6 months after AMI, regardless of whether the threshold value was set at 30, 40, 50 or 60% of the maximal isotope uptake in the early resting scan. CONCLUSIONS: Myocardial perfusion scintigraphy with adenosine-stress and resting MIBI-SPECT early after AMI underestimates myocardial viability in the majority of patients treated with thrombolytic agents. Neither reversible perfusion defects nor regional semi-quantitative perfusion data appear to predict spontaneous improvement of perfusion 6 months after AMI.

Adenosine↗
PubMed1998

Dedicated roles of plastid transketolases during the early onset of isoprenoid biogenesis in pepper fruits1.

Isopentenyl diphosphate (IPP), which is produced from mevalonic acid or other nonmevalonic substrates, is the universal precursor of isoprenoids in nature. Despite the presence of several isoprenoid compounds in plastids, enzymes of the mevalonate pathway leading to IPP formation have never been isolated or identified to our knowledge. We now describe the characterization of two pepper (Capsicum annuum L.) cDNAs, CapTKT1 and CapTKT2, that encode transketolases having distinct and dedicated specificities. CapTKT1 is primarily involved in plastidial pentose phosphate and glycolytic cycle integration, whereas CapTKT2 initiates the synthesis of isoprenoids in plastids via the nonmevalonic acid pathway. From pyruvate and glyceraldehyde-3-phosphate, CapTKT2 catalyzes the formation of 1-deoxy-xylulose-5-phosphate, the IPP precursor. CapTKT1 is almost constitutively expressed during the chloroplast-to-chromoplast transition, whereas CapTKT2 is overexpressed during this period, probably to furnish the IPP necessary for increased carotenoid biosynthesis. Because deoxy-xylulose phosphate is shared by the plastid pathways of isoprenoid, thiamine (vitamin B1), and pyridoxine (vitamin B6) biosynthesis, our results may explain why albino phenotypes usually occur in thiamine-deficient plants.

Amino Acid Sequence↗
PubMed1998

High prevalence of arrhythmias in elderly male athletes with a lifelong history of regular strenuous exercise.

OBJECTIVE: To characterise cardiac arrhythmias and cardiac autonomic function in 11 elderly men (mean (SD) age 73.2 (2.8) years) with a lifelong history of regular very strenuous, exercise. A control group of 12 healthy sedentary or moderately physically active men (74.5 (2.7) years) was also studied. DESIGN: 48 hour ambulatory electrocardiograms were recorded. Cardiac autonomic function was estimated from power spectral analysis of heart rate variability. Maximal oxygen uptake during treadmill exercise testing was 2.91 (0.52) l (41 (7) ml/kg). RESULTS: Nine of 11 athletes had complex ventricular arrhythmias compared with five of 12 controls. Seven athletes but none of the controls had episodes of heart rate below 40 beats/min and two athletes had RR intervals longer than two seconds. Heart rate variability in the athletes was higher than in the controls. CONCLUSIONS: Elderly athletes with a lifelong training history seem to have more complex arrhythmias and profound bradyarrhythmias than do healthy elderly controls, which may increase the risk of sudden cardiac death. In contrast, the age related decrease in heart rate variability seems to be retarded, which has a positive prognostic value and may decrease the risk of life threatening ventricular arrhythmias.

Aged↗
PubMed1997

Molecular analysis of carotenoid cyclase inhibition.

Later steps of carotenoid biosynthesis catalyzed by cyclase enzymes involve the formation of alpha, beta, and kappa-rings. Examination of the primary structure of lycopene beta-cyclase revealed 55% identity with that of antheraxanthin kappa-cyclase. Recombinant lycopene beta-cyclase afforded only beta-carotene, while recombinant antheraxanthin kappa-cyclase catalyzed the formation of beta-carotene from lycopene as well as the conversion of antheraxanthin into the kappa-carotenoid capsanthin. Since the formation of beta- and kappa-rings involves a transient carotenoid carbocation, this suggests that both cyclases initiate and/or neutralize the incipient carbocation by similar mechanisms. Several amine derivatives protonated at physiological pH were used to examine the molecular basis of this phenomenon. The beta-and kappa-cyclases displayed similar inhibition patterns. Affinity or photoaffinity labeling using p-dimethylamino-benzenediazonium fluoroborate, N,N-dimethyl-2-phenylaziridinium, and nicotine irreversibly inactivated both cyclase enzymes. Photoaffinity labeling using [3H]nicotine followed by radiosequence analysis and site-directed mutagenesis revealed the existence of two cyclase domains characterized by the presence of reactive aromatic and carboxylic amino acid residues. We propose that these residues represent the "negative point charges" involved in the coordination of the incipient carotenoid carbocations.

Affinity Labels↗
PubMed1997

Heart rate variability in healthy subjects is related to age and gender.

The effects of age and gender on heart rate variability as measured by spectral and time domain analysis of 24 h ECG recordings were evaluated in 101 healthy subjects, 49 men and 52 women (20-69 years of age). In the frequency domain, total power, very low-frequency power, low-frequency power and high-frequency power were negatively correlated to age (P < 0.001 for all variables). Total power decreased by 30% between 20-29 and 60-69 years of age. In the time domain, SDNN-index, the mean of the standard deviations of all normal R-R intervals for all 5 min segments of a 24 h ECG recording, was negatively correlated to age (P < 0.001). Total power, very low-frequency power, low-frequency power and the low-frequency/high-frequency ratio were lower in women (P < 0.05, P < 0.05, P < 0.01 and P < 0.01), although the absolute differences were much smaller than for age. There was a pronounced circadian variation; at night total power increased in all age groups (P < 0.01). The results show that age, and to a lesser degree gender, are important determinants of heart rate variability in healthy subjects. Heart rate variability is a valuable tool for risk stratification in cardiovascular disease, but the physiological effects of ageing, with diminishing heart rate variability in older age groups, must also be taken into account.

Adult↗
PubMed1997

High incidence of scintigraphic myocardial uptake defects at rest and during exercise in male elite runners.

OBJECTIVE: To evaluate the usefulness of myocardial perfusion scintigraphy (MIBI-SPECT) as a diagnostic tool in well trained men. DESIGN: The study was prospective, involving 2 d stress-rest myocardial scintigraphy (MIBI-SPECT), polar map reconstruction with and without uniform attenuation correction, and comparison with a healthy male group (local Swedish) and with a commonly used reference group (American, Emory University Hospital). SETTING: University Hospital, Stockholm, Sweden. SUBJECTS: 16 healthy, male elite runners (mean (SD) age 26.1 (3.1) years). Peak oxygen uptake 73 (4) ml O2/kg/min. RESULTS: Uptake defects on polar maps were found in the majority of the runners compared with both reference groups (local Swedish 13/16, American 10/16). Most defects (91%) were fixed. Defects were located in the anterior, lateral, and posterior regions of the left ventricle. Application of a uniform attenuation correction algorithm enhanced rather than reduced perfusion defect size, probably because this correction method is imperfect in SPECT studies of the thoracic cavity. CONCLUSIONS: If myocardial perfusion scintigraphy is used for evaluating well trained men, existing normal reference files for semiquantitative evaluation appear to be inadequate.

Adult↗
PubMed1996

Xanthophyll biosynthesis. Cloning, expression, functional reconstitution, and regulation of beta-cyclohexenyl carotenoid epoxidase from pepper (Capsicum annuum).

Pepper (Capsicum annuum) beta-cyclohexenyl xanthophyll epoxidase cDNA was cloned and the corresponding enzyme overexpressed and purified from Escherichia coli, for investigation of its catalytic activity. The recombinant protein did not directly accept NADPH for epoxidation of cyclohexenyl carotenoids, nor did it operate according to a peroxygenase-based mechanism. Instead, the reducing power of NADPH was transferred to the epoxidase via reduced ferredoxin as shown by reconstitution of epoxidase activity in the presence of NADPH, ferredoxin oxidoreductase, and ferredoxin. Bacterial rubredoxin could be substituted for ferredoxin. The pepper epoxidase acted specifically on the beta-ring of xanthophylls such as beta-cryptoxanthin, zeaxanthin, and antheraxanthin. The proposed reaction mechanism for epoxidation involves the formation of a transient carbocation. This characteristic allows selective inhibition of the epoxidase activity by different nucleophilic diethylamine derivatives, p-dimethylaminobenzenediazonium fluoroborate and N,N-dimethyl-2-phenylaziridinium. It was also shown that the epoxidase gene was up-regulated during oxidative stress and when chloroplasts undergo differentiation into chromoplasts in pepper fruit.

Amines↗
PubMed1996

Developmental and stress regulation of gene expression for plastid and cytosolic isoprenoid pathways in pepper fruits.

Plant cells synthesize a myriad of isoprenoid compounds in different subcellular compartments, which include the plastid, the mitochondria, and the endoplasmic reticulum cytosol. To start the study of the regulation of these parallel pathways, we used pepper (Capsicum annuum) fruit as a model. Using different isoprenoid biosynthetic gene probes from cloned cDNAs, we showed that only genes encoding the plastid enzymes (geranylgeranyl pyrophosphate synthase, phytoene synthase, phytoene desaturase, and capasanthin-capsorubin synthase) are specifically triggered during the normal period of development, at the ripening stage. This pattern of expression can be mimicked and precociously induced by a simple wounding stress. Concerning the cytosol-located enzymes, we observed that the expression of the gene encoding farnesyl pyrophosphate synthase is constitutive, whereas that of farnesyl pyrophosphate cyclase (5-epi-aristolochene synthase) is undetectable during the normal development of the fruit. The expression of these later genes are, however, only selectively triggered after elicitor treatment. The results provide evidence for developmental control of isoprenoid biosynthesis occurring in plastids and that cytoplasmic isoprenoid biosynthesis is regulated, in part, by environmental signals.

Amino Acid Sequence↗
PubMed1995

Identification of a plastid protein involved in vesicle fusion and/or membrane protein translocation.

Structural evidence has accumulated suggesting that fusion and/or translocation factors are involved in plastid membrane biogenesis. To test this hypothesis, we have developed an in vitro system in which the extent of fusion and/or translocation is monitored by the conversion of the xanthophyll epoxide (antheraxanthin) into the red ketocarotenoid (capsanthin). Only chromoplast membrane vesicles from red pepper fruits (Capsicum annuum) contain the required enzyme. Vesicles prepared from the mutant yellow cultivar are devoid of this enzyme and accumulate antheraxanthin. The fusion and/or translocation activity is characterized by complementation due to the synthesis of capsanthin and the parallel decrease of antheraxanthin when the two types of vesicles are incubated together in the presence of plastid stroma. We show that the extent of conversion is dependent upon an ATP-requiring protein that is sensitive to N-ethylmaleimide. Further purification and immunological analysis have revealed that the active factor, designated plastid fusion and/or translocation factor (Pftf), resides in a protein of 72 kDa. cDNA cloning revealed that mature Pftf has significant homology to yeast and animal (NSF) or bacterial (Ftsh) proteins involved in vesicle fusion or membrane protein translocation.

Amino Acid Sequence↗