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F Melandri

Publications and source records attributed to F Melandri.

12 recordsLinked to original sources
PubMed2001

[Recurrent acute myocardial infarction in a patient with nocturnal paroxysmal hemoglobinuria].

Paroxysmal nocturnal hemoglobinuria is a form of acquired hemolytic anemia with a high incidence of thrombotic complications, generally in the venous district; arterial thrombosis is rare, and exceptional in the coronary tree. We describe the case of a man who had two episodes of myocardial infarction, both during a hemoglobinuric crisis; this patient was free from cardiovascular risk factors and angiography revealed that there was no coronary stenosis. The clinical course was favorable and the patient's response to thrombolytic and dicumarol therapy was satisfactory. To our knowledge, this is the second case of coronary involvement in paroxysmal nocturnal hemoglobinuria described in the literature.

Hemoglobinuria, Paroxysmal↗
PubMed1999

Sepsis is associated with increased ubiquitinconjugating enzyme E214k mRNA in skeletal muscle.

Previous studies provided evidence that sepsis is associated with increased ubiquitin-proteasome-dependent protein breakdown in skeletal muscle. The 14-kDa ubiquitin-conjugating enzyme (E214k) has been proposed to be a key regulator of the ubiquitin proteolytic pathway. We tested the hypothesis that E214k message and protein levels are increased in skeletal muscle during sepsis. Sepsis was induced in rats by cecal ligation and puncture (CLP). Control rats were sham operated. E214k mRNA and protein levels were quantitated after Northern and Western blot analysis, respectively, 16 h after CLP or sham operation. Sepsis resulted in a 70% increase in the 1. 2-kb E214k transcript in the fast-twitch extensor digitorum longus muscle, whereas no changes were seen in the slow-twitch soleus muscle. E214k protein levels were not influenced by sepsis in any of the muscles studied. Although the changes in the expression of the E214k 1.2-kb transcript paralleled the differential effect of sepsis on protein breakdown in fast- and slow-twitch muscle, the potential role of E214k in the regulation of sepsis-induced muscle proteolysis needs to be interpreted with caution, because the results demonstrated that increased message levels were not associated with increased E214k protein levels.

Animals↗
PubMed1996

Kinetic studies on the inhibition of isopeptidase T by ubiquitin aldehyde.

Isopeptidase T (IPaseT) can hydrolyze isopeptide bonds of polyubiquitin (polyUb) chains, simple C-terminal derivatives of Ub, and certain peptides. We recently reported that IPaseT is regulated by ubiquitin (Ub); while submicromolar Ub activates, higher concentrations inhibit this enzyme [Stein et al. (1995) Biochemistry 34, 12616]. To explain these observations, we proposed a model for IPaseT involving two binding sites for Ub. According to the model, the two sites are adjacent to one another and are the extended active site that binds two Ub moieties of a polyUb chain. The "activation site" binds the Ub that donates Lys to the isopeptide bond. The "inhibition site" is adjacent and binds the Ub that donates the C-terminal Gly to the isopeptide bond. We now report that the interaction of IPaseT with the C-terminal aldehyde of Ub (Ub-H) is also modulated by Ub. In the absence of Ub, Ub-H inhibits IPaseT with a Ki of 2.3 nM, while at 0.6 microM Ub, where the "activation site" is occupied, Ki is less than 0.1 nM. At high Ub concentrations, where both the "activation" and "inhibition" sites are occupied, IPaseT cannot bind Ub-H. We also determined the kinetics of inhibition of IPaseT by Ub-H. In the absence of Ub, a two-step mechanism is followed. In the first step, Ub-H slowly combines with IPaseT to form a relatively weak complex (K1 = 260 nM) that slowly isomerizes to the final, stable complex that accumulates in the steady-state (k2 = 2 x 10(-3) s-1; k-2 = 0.02 x 10(-3) s-1). In contrast, Ub-activated IPaseT is inhibited by Ub-H through a three-step process. In the first step, Ub-H rapidly combines with IPaseT to form a complex (K1 = 10 nM) that slowly isomerizes to a second, more stable complex (k2 = 18 x 10(-3) s-1; k-2 = 1.5 x 10(-3) s-1). In the third step, the second complex converts to the final complex (k3 = 1.5 x 10(-3) s-1; k-3 < 0.2 x 10(-3) s-1). To unify the results of this study with our previous results on catalysis, we propose that binding of Ub either to catalytic transition states or to tetrahedral inhibition intermediates liberates more free energy than binding of Ub to the reactant state of IPaseT and that IPaseT can utilize this binding energy to stabilize both of these tetrahedral species. The overall effect is a Ub-induced increase in catalytic efficiency or inhibitory potency.

Animals↗
PubMed1996

Kinetic characterization of the chymotryptic activity of the 20S proteasome.

In this paper, we report kinetic studies for the chymotryptic activity of the 20S proteasome. Major observations include the following: (1) Reaction progress curves that are recorded at concentrations of Suc-Leu-Leu-Val-Tyr-AMC greater than about 40 microM are biphasic and characterized by initial velocities that decay by a first-order process to final, steady-state velocities. (2) Also at [Suc-Leu-Leu-Val-Tyr-AMC] > 40 microM, initial and steady-state velocities are smaller than predicted from simple, Michaelis-Menten kinetics. (3) The first-order rate constant for the approach to steady-state has a complex dependence on substrate concentration and decreases sigmoidally as substrate concentration increases. These results indicate that the 20S proteasome is a hysteretic enzyme and is subject to substrate inhibition. To explain these observations we propose a minimal kinetic model with two critical mechanistic features: (1) the 20S proteasome has two cooperative active sites for Suc-Leu-Leu-Val-Tyr-AMC and (2) there are two interconvertible conformers of active 20S proteasome. To probe this mechanism in greater detail, we explored the kinetic mechanism of inhibition of the 20S proteasome-catalyzed hydrolysis of Suc-Leu-Leu-Val-Tyr-AMC by the peptide aldehyde, Ac-Leu-Leu-Nle-H. Our studies reveal a nonlinear dependence of reciprocal steady-state velocity on inhibitor concentration (i.e., parabolic inhibition) as well as a nonlinear dependence of the apparent inhibitor dissociation constant on substrate concentration. Both of these observations are explained by binding of inhibitor at multiple sites on the enzyme. Taken together, the results of this study indicate that the 20S proteasome is a conformationally flexible protein that can adjust to the binding of ligands and that has multiple and cooperative active sites. These results support a view of the proteasome's substrate specificity in which (1) substrates are recognized and hydrolyzed by more than one active site; (2) each active site can bind substrates that possess a variety of P1 residues; and (3) the P1 residue plays a relatively minor role as a specificity determinant. Finally, we interpret the results of this study to suggest that, in vivo, the 20S proteasome requires conformational plasticity for its interactions with regulatory complexes and, after it has combined with appropriate regulatory complexes, to catalyze hydrolysis of proteins.

Amino Acid Sequence↗
PubMed1995

Kinetic studies of isopeptidase T: modulation of peptidase activity by ubiquitin.

We have investigated the specificity of isopeptidase T toward peptide-AMC substrates based on the C-termini of ubiquitin. The substrates investigated were Z-Gly-Gly-AMC, Z-Arg-Gly-Gly-AMC, Z-Leu-Arg-Gly-Gly-AMC, and Z-Arg-Leu-Arg-Gly-Gly-AMC and were hydrolyzed by isopeptidase T with kc/Km values of < 0.1, 1, 18, and 95 M-1 s-1, respectively. In the course of these experiments, we observed that the hydrolytic activity of isopeptidase T toward these substrates is modulated by ubiquitin in a biphasic fashion. While submicromolar concentrations of ubiquitin activate isopeptidase T, higher concentrations are inhibitory. In the activation phase, the extent of stimulation of kc/Km varies with substrate and is 8-, 50-, and 70-fold for Z-Arg-Gly-Gly-AMC, Z-Leu-Arg-Gly-Gly-AMC, and Z-Arg-Leu-Arg-Gly-Gly-AMC, respectively. Kd for ubiquitin in this phase is, of course, independent of substrate and equals 0.10 +/- 0.03 microM. At higher concentrations, ubiquitin is inhibitory and titrates kc/Km with an average Ki value of 3.0 +/- 1.3 microM for all three substrates. To explain these observations, we propose a structural model for isopeptidase T that involves two binding sites for ubiquitin. We propose that the two sites are adjacent to one another and are the extended active site that binds two ubiquitin moieties of a polyubiquitin chain for isopeptide bond hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Signal-induced site-specific phosphorylation targets I kappa B alpha to the ubiquitin-proteasome pathway.

The transcription factor NF-kappa B is sequestered in the cytoplasm by the inhibitor protein I kappa B alpha. Extracellular inducers of NF-kappa B activate signal transduction pathways that result in the phosphorylation and subsequent degradation of I kappa B alpha. At present, the link between phosphorylation of I kappa B alpha and its degradation is not understood. In this report we provide evidence that phosphorylation of serine residues 32 and 36 of I kappa B alpha targets the protein to the ubiquitin-proteasome pathway. I kappa B alpha is ubiquitinated in vivo and in vitro following phosphorylation, and mutations that abolish phosphorylation and degradation of I kappa B alpha in vivo prevent ubiquitination in vitro. Ubiquitinated I kappa B alpha remains associated with NF-kappa B, and the bound I kappa B alpha is degraded by the 26S proteasome. Thus, ubiquitination provides a mechanistic link between phosphorylation and degradation of I kappa B alpha.

Cysteine Endopeptidases↗
PubMed1995

[Physiopathology of vasovagal syncope: review of the most endorsed theories and recent findings].

Vasovagal syncope is associated with an abnormal reflex and the physiopathological mechanisms of the phenomenon overall are only partially known. Experimental and clinical studies suggest that the main factor which triggers the syncope is the brusque interruption of the alpha-adrenergic tone with marked, sudden peripheral vasodilation. Although documented, vagal hypertony, with consequent bradycardia and asystolia, is only occasional and is almost always a secondary phenomenon. The most commonly suggested cause of vasovagal syncope is a Bezold-Jarish reflex starting from the cardiac receptors in the walls of the ventricle, mediated by the paradoxical activation of afferent vagal fibres. However, recent studies are suggesting that there may be other pathogenetic mechanisms such as the paradoxical activation of the venous-atrial baroceptors and other "extracardiac" vascular receptors. The neuro-endocrine aspect of the vasovagal reaction is very complex and in spite of the many studies carried out on the catecholamine, renal-angiotensive system, arginine-vasopressin, and b-endorphine trends, there are still many points awaiting clarification. The response of the autonomous nervous system linked to age also require further research.

Age Factors↗
PubMed1985

[Primary angiosarcoma of the right atrium invading the pericardial cavity. Description of a case diagnosed by exploratory thoracotomy and surgically treated with success].

The AA. report the case of a 43-year-old woman with an angiosarcoma arising from the right atrial wall and growing into the pericardial cavity. The patient presented with recurrent pericardial effusion initially responsive to medical therapy. The diagnosis was made at the exploratory thoracotomy. Repeated 2D-Echocardiograms did not help for the diagnosis in this particular case. The patient underwent surgical resection of the tumor, chemo- and radiotherapy. After 30 months there are no signs of recurrence or metastasis. In our opinion the frequent recurrence of pericardial effusion in the same patient should be regarded with special suspicion.

Adult↗