Biomedical subjects

Massimo Pomponi

Publications and source records attributed to Massimo Pomponi.

4 recordsLinked to original sources

PubMed2006

Interaction between EDTA and sodium hypochlorite: a nuclear magnetic resonance analysis.

Recent studies detected erosion of the dentinal walls following the use of EDTA as a final flush. Several authors have studied degradation of EDTA and it appears to be caused by an oxidation reaction. The objective of this paper was to verify through nuclear magnetic resonance (NMR) analysis if the oxidizing property of sodium hypochlorite inactivates EDTA. Solutions of sodium hypochlorite and EDTA were analyzed. EDTA tracing and the appearance of new signals indicative of by-products of the reaction, were studied at different time intervals with a NMR analysis. The tracings of NMR analysis confirmed that the reaction between sodium hypochlorite and EDTA lead to a very slow but progressive degradation of this compound. Mindful of the limitations of an in vitro study, the results of this study nevertheless demonstrated that a final flush with sodium hypochlorite cannot limit the chelating effects of EDTA in a clinically realistic time period.

Chelating Agents↗

PubMed2004

Hemoglobin, pH and DPG/chloride shifting.

In this study a decreased DPG response by polar bear (Ursus maritimus) hemoglobin was observed, and this response was interpreted as an example of gradual DPG/chloride shifting. This sort of mechanism has been suggested to occur in ruminants and, intuitively, one might guess that for ruminants the DPG/Cl- shifting might have been beneficial and hence selected for at the time of the latest Ice Age. However, suggestion that this is purely a temperature effect in polar bears and ruminants conflicts with the existence, in the hot savanna, of mammals that have Hb modulated by chloride. However, acidosis effects caused by routine periods of food shortage, induced in extreme environments may explain the responses of the hemoglobins of animals adapted to extreme habitats. The chloride effect is bound to specific amino acid substitutions in key positions. In polar bear Hb, they are specific, additional (with respect to human HbA) O2-linked chloride binding sites located between Lys-76 (beta) and Lys-8 (beta). The amino acids operate as an additional H+ binding site for a chloride anion. Additionally, with respect to human adult HbA, the primary structure of polar bear Hb was characterized by two substitutions in beta chains: Pro-5 (A2)--> Gly and Ala-76 (E20)-->Lys. The increased flexibility of the A helix causes the lower DPG effect. We further hypothesize that the resulting widening of the central cavity allows the Lys-82 (beta) terminus to be free and constitute an additional, chloride-binding site.

Amino Acid Sequence↗

PubMed2002

Inhibition of acetylcholinesterase by physostigmine analogs: conformational mobility of cysteine loop due to the steric effect of the alkyl chain.

The effect of a series of physostigmine analogs on acetylcholinesterase activity was investigated. The second-order rate constant k(on) of the enzyme-inhibitor complex correlates with the conformational positioning of aromatic residues, especially Trp84, in the transition state complex. The van der Waals interactions are an important structural element of this conformational change. A transient mobility of the cysteine loop (Cys67-Cys94) was confined only to the presence of a significant steric effect. Even with this limitation, however, the steric effect seems to be an appropriate model for future tests on the "back door" hypothesis involving facilitated opening for faster product clearance.

Acetylcholinesterase↗

PubMed2002

Polar bear hemoglobin and human Hb A0: same 2,3-diphosphoglycerate binding site but asymmetry of the binding?

Polar bear (Ursus maritimus) hemoglobin (Hb) shows a low response to 2,3-diphosphoglycerate (2,3-DPG), compared to human Hb A0, even though these proteins have the same 2,3-DPG-binding site. In addition, polar bear Hb shows a high response to chloride and an alkaline Bohr effect (deltalog P50/deltapH) that is significantly greater than that of human Hb A0. The difference in sequence Pro (Hb A0)-->Gly (polar bear Hb) at position A2 in the A helix seems to be critical for reduced binding of 2,3-DPG. Our results also show that the A2 position may influence not only the flexibility of the A helix, but that differences in flexibility of the first turn of the A helix may affect the unloading of oxygen for the intrinsic ligand affinities of the alpha and beta chains. However, preferential binding to either chain can only take place if there is appreciable asymmetric binding of the phosphoric effector. Regarding this point, 31P NMR data suggest a loss of symmetry of the 2,3-DPG-binding site in the deoxyHb-2,3-DPG complex.

2,3-Diphosphoglycerate↗