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A Desideri

Publications and source records attributed to A Desideri.

At least 91 records · Page 5Linked to original sources
PubMed1998

Dipyridamole stress echocardiography and exercise testing for risk stratification after uncomplicated myocardial infarction.

BACKGROUND: Risk stratification for subsequent cardiac events after an acute infarction can be obtained by exercise testing or dipyridamole stress echocardiography. It remains to be determined whether these modalities are equivalent and provide incremental information on top of clinical evaluation. The aim of our study was to compare the prognostic information obtained early after an acute uncomplicated myocardial infarction of high dose dipyridamole coupled with echocardiography (stress echo) or maximal symptom-limited exercise testing. METHODS AND RESULTS: Ninety patients underwent dipyridamole stress echo and exercise testing at a mean +/- SD of 9 +/- 4 days after admission for acute uncomplicated first myocardial infarction. All patients were prospectively followed for 22 +/- 16 months. There were 9 hard events (3 cardiac deaths and 6 acute myocardial infarctions) and 12 soft events due to post MI angina (6 angioplasty and 6 bypass surgery procedures). Univariate predictor of hard events was rest-stress wall motion score index variation (p = 0.009); univariate predictors of all events (hard + soft) were: positive exercise testing (p = 0.001), positive stress echo (p = 0.001), rest-stress wall motion score index variation (p = 0.002), extent of ischemia at echo (p = 0.008). Multivariate analysis by Cox selected a non-Q wave infarction and rest-stress wall motion score index variation as predictors of death or reinfarction (overall chi-square for the model 12.2, p = 0.0022). CONCLUSIONS: Stress echo is superior to ergometric variables for predicting events after uncomplicated myocardial infarction.

Aged↗
PubMed1997

Evidence of his61 imidazolate bridge rupture in reduced crystalline Cu,Zn superoxide dismutase.

X-ray absorption spectroscopy has been carried out on the copper K edge in oxidized and reduced bovine Cu,Zn SOD in solution and in crystalline state. The results indicate that the copper coordination geometry is unaffected by the solution or by the crystalline state of the protein, in both oxidation states. Moreover the two oxidation states of the active copper ion are reflected under, all the experimental conditions, by distinct coordination spheres around the catalytic metal, which is four-coordinated and three-coordinated in the Cu(II) and in the Cu(I) enzyme, respectively.

Absorptiometry, Photon↗
PubMed1997

Unique structural features of the monomeric Cu,Zn superoxide dismutase from Escherichia coli, revealed by X-ray crystallography.

The first three-dimensional structure of a functional monomeric Cu, Zn superoxide dismutase (from Escherichia coli, E_SOD) is reported at 2.0 A resolution (R-factor=16.8%). Compared to the homologous eukaryotic enzymes, E_SOD displays a perturbed antiparallel beta-barrel structure. The most striking structural features observed include extended amino acid insertions in the surface 1, 2-loop and S-S subloop, modification of the disulfide bridge connection, and loss of functional electrostatic residues, suggesting a modified control of substrate steering toward the catalytic center. The active site Cu2+ displays a distorted coordination sphere due to an unusually long bond to the metal-bridging residue His61. Inspection of the crystal packing does not show regions of extended contact indicative of a dimeric assembly. The molecular surface region involved in subunit dimerization in eukaryotic superoxide dismutases is structurally altered in E_SOD and displays a net polar nature.

Amino Acid Sequence↗
PubMed1997

Effect of Val 73 --> Trp mutation on the reaction of "cambialistic" superoxide dismutase from Propionibacterium shermanii with hydrogen peroxide.

The H2O2 inactivation of the "cambialistic" superoxide dismutases from Propionibacterium shermanii, which is active with either iron or manganese at the active site, has been studied in the native and Val 73 --> Trp mutant enzymes. The wild-type iron-containing form of this enzyme is much more resistant to treatment with H2O2 with respect to the other metal-specific Fe superoxide dismutase isoenzymes. After incubation with high amounts of H2O2 the enzyme maintains more than 40% of the initial activity. The activity of the Val 73 --> Trp mutant drastically decreases to less than 5% of the initial activity after incubation with hydrogen peroxide. Amino acid analysis of the H2O2-treated mutant enzyme evidenced the loss of the Trp 73 residue which is shown to play a critical role in the stabilization of the monomer fold of the enzyme. On the other hand, the manganese-containing wild-type and mutant enzymes were completely resistant toward H2O2 demonstrating the specific role of iron in the inactivation process.

Binding Sites↗
PubMed1997

Comparative stability studies on the iron and manganese forms of the cambialistic superoxide dismutase from Propionibacterium shermanii.

The superoxide dismutase of Propionibacterium shermanii shows similar activity with iron and manganese bound at the active site of the protein. On the other hand, the iron form, in comparison to the manganese form, exhibits higher stability towards thermal- and pH-dependent inactivation. Upon inactivation the metal ions are released from the active site. Thus, in comparison to the manganese form, a higher stability of the iron-protein complex might be the triggering reason for this behavior.

Ammonium Sulfate↗
PubMed1997

Spectroscopic characterization of recombinant Cu,Zn superoxide dismutase from Photobacterium leiognathi expressed in Escherichia coli: evidence for a novel catalytic copper binding site.

Cu,Zn superoxide dismutase from Photobacterium leiognathi has been cloned and expressed in Escherichia coli. The circular dichroism spectrum in the UV region of the recombinant protein indicates an higher content of random coil structure with respect to the eukaryotic enzymes. Investigation of the active site by optical, CD, and EPR spectroscopy indicates a different coordination geometry around the catalytic copper site with respect to the eukaryotic enzymes. In particular a different orientation of the metal bridging histidine is suggested. The pH dependence of the copper EPR spectrum shows the presence of a single equilibrium which is at least one unit lower than the pK value observed for the bovine enzyme. Despite such structural differences the catalytic rate of this enzyme is identical to that observed for the eukaryotic Cu,Zn superoxide dismutase, suggesting that the overall electric field distribution is similar to that observed in the eukaryotic enzymes.

Animals↗
PubMed1997

Exercise technetium 99m sestamibi single-photon emission computed tomography late after coronary artery bypass surgery: long-term follow-up.

BACKGROUND AND HYPOTHESIS: The prognostic value of exercise technetium 99m sestamibi single-photon emission computed tomography (SPECT) imaging in patients with previous bypass surgery is unknown. The aim of our study was to assess the prognostic information obtained with exercise scintigraphy performed for routine follow-up or reappearance of symptoms. METHODS: We studied 75 patients referred to our Center at a mean of 38 +/- 53 months from the revascularization procedure and prospectively followed them for 38 +/- 24 months. RESULTS: Fifteen patients (20%) had events at follow-up: there were 4 cardiac deaths, 3 nonfatal acute myocardial infarctions, 8 late revascularization procedures (4 percutaneous transluminal angioplasty and 4 repeat bypass surgery). Univariate analysis identified a history of typical angina (p = 0.001), a clinically positive ergometric test (p = 0.009), peak exercise heart rate (p = 0.0003), percentage of maximal predicted heart rate (p = 0.0001), peak exercise double product (p = 0.048), therapy during exercise (p = 0.003), scintigraphic summed reversibility score (i.e., the summation of the segmental differences between stress and rest) (p = 0.014), as significant predictors of events. Three multivariate models were built, with clinical variables (Model 1, chi square 15.97), ergometric variables (Model 2, chi square 19.66), and with scintigraphic variables added to clinical/ergometric variables (Model 3, chi square 31.13). The scintigraphic variable selected in the model as significant predictor of events was the summed reversibility score (p = 0.008). CONCLUSIONS: Exercise sestamibi SPECT scintigraphy provides optimal prognostic information after clinical and ergometric parameters in patients with previous bypass surgery.

Adult↗
PubMed1997

Solvent effects on the distribution of conformational substates in native and azide reacted Cu, Zn superoxide dismutase. An EPR study.

Native and azide reacted Cu, Zn superoxide dismutase in aqueous and mixed water-glycerol solution have been investigated by EPR spectroscopy at low temperature. An accurate computer simulation, based on a well established theoretical model which has been reformulated for rhombic symmetry, has shown that the EPR spectrum of the copper ion in the native protein shows a significant g and A strain in the parallel region. The strain arises from a distribution of the ligand field strengths onto the metal ion and this could be traced back to the existence of a multiplicity of conformational states in the protein molecule. The strain is reduced in the presence of azide which is known to bind directly to the copper atom and to give rise to a more relaxed configuration corresponding to a square pyramidal geometry in which the apical ligand occupies an elongated position. In both samples, addition of glycerol further reduces the strain, indicating that the solvent is directly coupled to the protein matrix, thereby modulating the structural heterogeneity displayed by the protein molecule.

Azides↗
PubMed1997

The essential dynamics of Cu, Zn superoxide dismutase: suggestion of intersubunit communication.

A 300-ps molecular dynamics simulation of the whole Cu, Zn superoxide dismutase dimer has been carried out in water, and the trajectory has been analyzed by the essential dynamics method. The results indicate that the motion is defined by few preferred directions identified by the first four to six eigenvectors and that the motion of the two monomers at each instant is not symmetrical. The vectors symmetrical to the eigenvectors are significantly sampled, suggesting that, on average, the motions of the two subunits will exchange. Large intra- and intersubunit motions involving different subdomains of the protein are observed. A mechanical coupling between the two subunits is also suggested, because displacements of the loops surrounding the active site in one monomer are correlated with the motion of parts of the second toward the intersubunit interface.

Computer Simulation↗
PubMed1997

Characterization of Cu,Zn superoxide dismutase from the bathophile fish, Lampanyctus crocodilus.

Cu,Zn SOD from the bathophile teleost Lampanyctus crocodilus (LSOD) shows a high degree of homology with the sequence of the enzymes from other teleostean fish species. The catalytic properties of LSOD are very similar to those of the bovine enzyme, albeit with higher sensitivity to thermal denaturation. The apparent molecular mass of LSOD (37.6 KDa) is higher than the other Cu,Zn SOD variants studied. The aminoacid sequence of LSOD reveals interesting substitutions compared to the bovine enzyme. These are discussed in view of the particular environmental conditions to which L. crocodilus is adapted.

Amino Acid Sequence↗
PubMed1997

Effect of Lys175 mutation on structure function properties of Propionibacterium shermanii superoxide dismutase.

The role of electrostatic factors in the enzyme-substrate encounter process of manganese and iron containing superoxide dismutases has been studied in the enzyme from Propionibacterium shermanii by chemical neutralization of lysine residues and site-directed mutagenesis of the highly conserved residue Lys175. Lysine residues have been neutralized by carbamoylation and Lys175 has been selectively replaced by isoleucine and arginine. Catalytic measurements show a dramatic decrease of the activity in the chemically modified enzyme. Electrostatic potential calculations evidence in the modified enzyme a large contraction of the positive potential areas which surround the active sites in the native enzyme, indicating that electrostatic factors are critical in the enzyme-substrate encounter process of Mn- and Fe-superoxide dismutases. The activity drastically decreases also in Lys175-->Ile but not in the Lys175-->Arg mutant. Brownian dynamics simulations indicate that the decrease of activity in the Lys175-->Ile mutant cannot be due only to a decrease of the enzyme-substrate association rate, suggesting that Lys175 plays a relevant role also in the structural stabilization of the active site.

Binding Sites↗
PubMed1997

[Echocardiography or stress scintigraphy with dipyridamole for the stratification of risk after acute myocardial infarction?].

UNLABELLED: Increased risk of subsequent cardiac events after an acute infarction can be identified through dipyridamole infusion. It remains to be determined whether echocardiographic or scintigraphic imaging modes are equivalent. The aim of our study was to compare the prognostic information obtained early after an acute uncomplicated myocardial infarction through high-dose dipyridamole coupled with echocardiography or scintigraphy via Tc 99m sestamibi SPECT imaging. METHODS AND RESULTS: Fifty-one patients underwent simultaneous dipyridamole stress echocardiography and scintigraphy at a mean +/- SD of 12 +/- 3 days after admission for acute uncomplicated myocardial infarction. A subgroup of 44 patients performed exercise testing according to maximal symptom limited protocol. All patients were followed prospectively for 346 +/- 273 days (range 11-959). Cardiac events occurred in 20 patients (39%), and 1 death, 2 myocardial reinfarctions and 17 cases of unstable angina were recorded. Univariate predictors of cardiac events were: positive dipyridamole echo (p < 0.001), ischemia in the infarct zone or in remote zones by echo (p < 0.001), ejection fraction < 40% (p = 0.042) and positive exercise testing (p = 0.003). Risk was best predicted by multivariate Cox analysis on the basis of 1) ischemia in remote zones by dipyridamole echo (p < 0.001) and 2) ischemia in the infarct zone by dipyridamole echo (p = 0.003), blood pressure at peak exercise < 150 mmHg (p = 0.010) and non-Q wave infarction (p = 0.003). CONCLUSIONS: Echocardiographic imaging during dipyridamole infusion is superior to sestamibi scintigraphy for predicting events after uncomplicated myocardial infarction.

Aged↗
PubMed1996

Diving behaviour and haemoglobin function: the primary structure of the alpha- and beta-chains of the sea turtle (Caretta caretta) and its functional implications.

The amino acid sequence of the alpha- and beta-chains of haemoglobin (Hb) from the loggerhead sea turtle (Caretta caretta) has been determined. Comparison with that of human Hb shows differences in several residues involved in both alpha 1 beta 1 and alpha 1 beta 2 packing contacts. On the whole, in spite of the mutations, the essential characteristics of both interfaces seem to be maintained. The functional properties of the sea turtle Hb have been investigated at different temperatures and as a function of proton, chloride and organic phosphate concentrations. In addition to overall similarities shared with most of the vertebrate Hbs previously described, this molecule shows significant differences which could be related to the life behaviour of the turtle. In fact, while the shape of the Bohr-effect curve is well adapted for gas exchange during prolonged dives, the very small enthalpy change for O2 binding ensures that O2 delivery becomes essentially insensitive to the temperature changes of the environment. Moreover, and similarly to the case of emperor penguin Hb, the small alkaline Bohr effect appears to be only choride-linked, since the pH dependence of the O2 affinity is abolished in the absence of this ion. These functional characteristics are discussed on the basis of the primary structure of alpha- and beta-chains.

Adaptation, Physiological↗
PubMed1996

Azide, cyanide, fluoride, imidazole and pyridine binding to ferric and ferrous native horse heart cytochrome c and to its carboxymethylated derivative: a comparative study.

Azide, cyanide, fluoride, imidazole, and pyridine binding to ferric and ferrous native horse heart cytochrome c and to its carboxymethylated derivative has been investigated, from the thermodynamic viewpoint, at pH 7.5 and 25.0 degrees C. Ligand affinity for ferric and ferrous carboxymethylated cytochrome c is higher by about 30- and 400-fold, respectively, than that observed for the native protein. The results here reported: (i) allow the estimation, for the first time, of the ligand-independent free energy associated with the heme-iron sixth coordination bond in ferric and ferrous native cytochrome c, which turns out to be +8.4 kJ mol-1 and +14.6 kJ mol-1, at 25.0 degrees C, respectively, and (ii) suggest an interplay between redox, structural, ligand binding, and recognition properties of cytochrome c.

Animals↗
PubMed1996

Characterization of the binding of Fe(III) to F1ATPase from bovine heart mitochondria.

The binding Fe(III) to F1ATPase purified from beef heart mitochondria has been characterized by chemical analyses and EPR spectroscopy. F1ATPase binds 2 mol of Fe(III)/mol of protein selectively in the presence of saturating concentrations of ATP. In the absence of nucleotides or in the presence of either saturating ADP or limiting ATP concentrations, the enzyme binds 1 equivalent of Fe(III). F1ATPase pretreated with 5'-p- fluorosulfonylbenzoyladenosine, that selectively modifies the non-catalytic sites, binds only 1 mol of Fe(III)/mol of protein in the presence of either saturating ATP or ADP, Fe(III)-loaded F1ATPase containing either 1 or 2 equivalents of Fe(III) show identical EPR signals at g=4.3. The signals are not perturbed by the binding of nucleotides to the enzyme while they are altered by phosphate addition. These results indicate that F1ATPase contains two distinct Fe(III)-binding sites, which differ from nucleotide-binding sites, and that one of these sites is opened up for Fe(III) uptake by conformational changes induced by binding of ATP to the loose non-catalytic site.

Adenosine Diphosphate↗
PubMed1996

Three-dimensional structure of Xenopus laevis Cu,Zn superoxide dismutase b determined by X-ray crystallography at 1.5 A resolution.

Xenopus laevis Cu,Zn superoxide dismutase (recombinant isoenzyme b) has been crystallized and the structure determined at 1.49 A resolution. The crystals belong to space group P2(1)2(1)2(1), with cell constants a = 73.33, b = 68.86, c = 59.73 A, and contain one dimeric molecule of M(r) 32 000 per asymmetric unit. The structure was solved by molecular-replacement techniques using the semisynthetic Cu,Co bovine enzyme as search model, and refined by molecular dynamics with a crystallographic pseudo-energy term. During the final steps, positional and anisotropic thermal parameters of the atoms were refined. The R factor for the 49 209 unique reflections in the 10.0-1.49 A resolution range is 0.104, for a model comprising 2023 protein atoms, two Cu(2+), two Zn(2+), and 353 water molecules. The overall temperature factor for the model, including solvent, is 20.3 A(2), while the calculated r.m.s. coordinate error for the refined model is 0.036 A. As suggested by the primary structure homology to any other known intracellular eukaryotic superoxide dismutase (> 50%), the typical structural scaffolding of flattened antiparallel eight-stranded (beta-barrel is well conserved in X. laevis Cu,Zn superoxide dismutase b, together with the coordination geometry of the metal centers in the active site. The higher thermal stability of the bb X. laevis superoxide dismutase homodimer, with respect to dimers involving the a-type isoenzyme subunit(s), can be related, on the basis of the high-resolution structure, to side-chain and solvent interactions centered on residue Tyr149, in both b-type subunits. The analysis of the overall solvent structure reveals a number of equivalent water molecule sites in the two subunits, and in homologous superoxide dismutase models. Their locations are discussed in detail and classified on the basis of their structural role.

Journal Article↗