Maria Elisabetta Clementi

Functional Modulation by Lactate of Myoglobin A MONOMERIC ALLOSTERIC HEMOPROTEIN

The effect of lactate on O2 binding properties of sperm whale and horse heart myoglobins (Mb) has been investigated at moderately acid pH (i.e. pH 6.5, a condition which may be achieved in vivo under a physical effort). Addition of lactate brings about a decrease of O2 affinity (i.e. an increase of P50) in sperm whale and horse heart myoglobins. Accordingly, lactate shows a different affinity for the deoxygenated and oxygenated form, behaving as a heterotropic modulator. The lactate effect on O2 affinity appears to differ for sperm whale and horse heart Mb, δlogP50 being ≈1.0 and ≈0.4, respectively. From the kinetic viewpoint, the variation of O2 affinity for both myoglobins can be attributed mainly to a decrease of the kinetic association rate constant for ligand binding.

Aβ(31–35) peptide induce apoptosis in PC 12 cells: Contrast with Aβ(25–35) peptide and examination of underlying mechanisms

Abstract The toxic behaviour of the two shorter sequences of the native Aβ amyloid peptide required for cytotoxicity i.e., Aβ(31–35) and Aβ(25–35) peptides, was studied. We have shown that Aβ(31–35) peptide induces neurotoxicity in undifferentiated PC 12 cell via an apoptotic cell death pathway, including caspase activation and DNA fragmentation. Aβ(25–35) peptide, like the shorter amyloid peptide has the ability to induce neurotoxicity, as evaluated by the MTS reduction assay and by adherent cell count, but the Aβ(25–35) peptide-induced neurotoxicity is not associated with any biochemical features of apoptosis. The differences observed between the neurotoxic properties of Aβ(31–35) and Aβ(25–35) peptides might result on their different ability to be internalised within the neuronal cells. Furthermore, this study reveals that the redox state of methionine residue, C-terminal in Aβ(31–35) and Aβ(25–35) peptides affect in a different way the toxic behaviour of these two short amyloid fragments. Taken together our results suggest that Aβ(31–35) peptide induces cell death by apoptosis, unlike the Aβ(25–35) peptide and that role played by methionine-35 in Aβ induced neurotoxicity might be related to the Aβ aggregation state.

Synergistic modulation by chloride and organic phosphates of hemoglobin from bear (Ursus arctos)

The oxygen binding properties of hemoglobin (Hb) from brown bear (Ursus arctos) have been studied focussing on the effect of heterotropic ligands, and the behaviour has been compared with that of human HbA, taken as a prototype of mammalian Hbs. It has been observed that in bear Hb chloride ions and 2,3-diphosphoglyceric acid (Gri(2,3)P2) can modulate the oxygen affinity in a synergistic way such that their individual effect is enhanced whenever they are both present in saturating amounts. The thermodynamic analysis of such a feature indicates that in bear Hb there are two classes of chloride binding sites, one acting synergistically with Gri(2,3)P2 and another one, which likely overlaps with the organic phosphate interaction cleft, and is therefore fully operative only in the absence of Gri(2,3)P2. The behaviour of the last site is similar to that observed in human HbA, where the effect of Cl- and Gri(2,3)P2 is mutually exclusive. The interaction energy between chloride and Gri(2,3)P2 synergistic binding sites appears to be O2-linked so that the interplay may have a relevant physiological role in modulating the oxygen transport in brown bear. This behaviour is associated with a marked pH-dependence of the oxygenation enthalpy in bear Hb, such that under acidotic and hypercloruremic conditions, oxygen supply to peripheral tissues could be maintained essentially unaltered even under low temperature conditions.

Arctic life adaptation--III. The function of whale (Balaenoptera acutorostrata) hemoglobin

1. The oxygen binding properties of the hemoglobin from the Lesser Rorqual, Balaenoptera acutorostrata, has been investigated with respect to the possible effects of organic phosphates on gas transport in arctic environments. 2. The intrinsic oxygen affinity of the hemoglobin is high and strongly modulated by the effects of organic phosphates. 3. In the absence of organic phosphates, the temperature sensitivity of oxygen binding expressed by the heat of oxygenation, delta H, is -16.2 kcal/mol when corrected for the heat of oxygen in solution. 4. In the presence of organic phosphates there is a marked decrease in the temperature sensitivity delta H approximately -5 kcal/mol). 5. This feature is of great importance for oxygen unloading in the flippers and the tail, where the temperature is lower than the trunk of the whale. 6. Furthermore the organic phosphates strongly increase the Bohr coefficient, delta log P50/delta pH, from less than -0.3 in stripped hemoglobin to about -1.5 when the hemoglobin is saturated with P6-inositol. 7. This feature may be of great physiological importance by reducing the CO2 tension and acidosis after a prolonged dive.

Selective Binding of Met-Hemoglobin to Erythrocytic Membrane: A Possible Involvement in Red Blood Cell Aging

It is well known that in vivo and under normal physiological conditions intraerythrocytic hemoglobin may exist in three different forms represented by oxygenated, deoxygenated and partially oxidized hemoglobin (1–4). Apart from the first two derivatives whose relative proportions are continuously changing during the oxygenation deoxygenation cycle, met-hemoglobin is normally present at a steady-state level of about 1%.

S100b induces expression of Myoglobin in APβ treated neuronal cells in vitro: a possible neuroprotective mechanism.

BACKGROUND In this study, human neuroblastoma cells (IMR32) treated with Amyloid Beta Peptide (APβ), were used as model to evaluate the molecular basis of protective role of S100b, a neurotrophic factor and neuronal survival protein, highly expressed by reactive astrocytes close to amyloid deposition in the cortex of Alzheimers patients. The aim of this work is to value the effect of S100b on ROS production in cells treated with Amyloid Beta Peptide and the subsequent influence on globin gene expression. METHOD In this study we investigated the effect of S100b on ROS production and on globin gene expression in human neuroblastoma cells (IMR32) treated with Amyloid Beta Peptide (APβ). RESULTS Our results have shown that at nanomolar concentrations, S100b protects cells against AP. mediated cytotoxicity and the protective mechanism could be related, almost in part, to the control of ROS production through an over expression of Myoglobin gene. CONCLUSION In light of our results, we speculate that over-expression of the Myoglobin gene could be read as a possible attempt of the cell to increase the scavengers of reactive oxygen species (ROS).

Flight and heat dissipation in migratory birds

The effect of temperature on the functional properties of hemoglobins from two different species of birds,i.e. Gallinula chloropus and Columba livia, has been investigated. These two species are characterized by different life-behaviour, sinceGallinula chloropus is seasonally subjected to prolonged flights, whileColumba livia although flying at a quite high velocity (~50 Km/h) is not able to maintain the corresponding muscular activity for more than 10 minutes. The results reported in this paper suggest that in some migratory species, special molecular mechanisms may increase heat dissipation and stabilize the body temperature at a reasonable level. In fact birds, during normal sustained flight, must be able to dissipate more than eight times as much heat as during rest in order not to be overheated.RiassuntoIn questaNota abbiamo voluto esaminare l’effetto della temperatura sulle proprietà funzionali dell’emoglobina di due differenti specie di uccelli, laGallinula chloropus e laColumba livia. Il primo è un uccello migratore stagionale, soggetto a voli intensi e prolungati, mentre il secondo, sebbene raggiunga alte velocità (~ 50 Km/h), non è in grado di volare per più di 10 minuti a causa dei fenomeni di surriscaldamento. I risultati ottenuti sembrano dimcstrare come in alcune specie migratorie esistano speciali meccanismi molecolari in grado di aumentare la dissipazione di calore prodotto durante il volo e di stabilizzare la temperatura corporea.