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Biomedical subjects

E Antonini

Publications and source records attributed to E Antonini.

At least 55 records · Page 3Linked to original sources
PubMed1981

Equilibrium and kinetic evidence for a transition between six- and five-coordinate ferrous heme in the nitric oxide derivative of Aplysia myoglobin.

The pH dependence in the range 3--7 of the optical absorption and electron paramagnetic resonance of the nitric oxide adduct of ferrous Aplysia myoglobin is reported. Optical spectra in the Soret region show a transition between two conformers with an apparent pK in the range 3.5--5 depending on the presence of carboxylic anions as third component. In the same pH range, the EPR spectrum undergoes a change from a 9-line to a 3-line hyperfine pattern in the g. region, similar to that reported for synthetic heme derivatives and for other hemoproteins. The structural interpretation of the pH-induced transition experienced by Aplysia myoglobin nitric oxide is that of a proton-linked cleavage of the proximal bond as suggested by several lines of evidence. Temperature-jump measurements allowed an estimation of the relaxation time for the process, which is of the order of 0.3 ms at 25 degrees C.

Animals↗
PubMed1981

Steady-state and pre-steady-state kinetics of the trypsin-catalysed hydrolysis of alpha-CBZ-L-lysine-p-nitrophenyl ester.

The catalytic properties of bovine tyrpsin (EC 3.4.21.4) have been investigated using a synthetic chromogenic substrate: alpha-CBZ-L-lysine-p-nitrophenyl ester (ZLNPE). The use of ZLNPE allows the determination of trypsin down to a concentration of 2 . 10(-9) M. Steady-state and pre-steady-state data have been in the framework of the minimum three-step mechanism: (Formula: see text). The pH-dependence of the kinetic parameters shows that at acid pH values (congruent to 2.6) the k+3 step is rate limiting in catalysis, whereas for pH values higher than 4.8 k+2 becomes rate limiting. This change in rate-limiting step with pH illustrates the danger in the assumption that kcat vs. pH profiles for protease action on substrates with good leaving groups are equivalent to k+3 vs. pH profiles.

Animals↗
PubMed1981

A plausible two-state model for cytochrome c oxidase.

The catalytic properties of pulsed and resting cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1), expressed in terms of a minimal kinetic scheme and simulated by numerical computations, were successfully described. A two-state model, in which the relative amounts of the enzyme present in each conformation are regulated by the rates of electron flux and O2 binding on one side and the interconversion rates on the other, accounts for the activation of cytochrome c oxidase during turnover.

Electron Transport Complex IV↗
PubMed1981

Distribution and respiratory properties of sheep hemoglobins A and B containing the II alphaHis chain.

We recently reported the discovery of a second alpha chain, differing from the common alpha chain by the replacement 113 (or 114) Leucine leads to Histidine, in the hemoglobin of several domestic sheep. The ratio of the common alpha chain, here called alpha Leu, to the variant one, here called II alpha His, was either about 1.8:1 or about 4:1. In this study, the distribution of the II alpha His chain in 217 sheep from 8 domestic breeds was investigated: the II alpha His chain is present in 30% of animals from different breeds. Oxygen equilibrium determination showed no differences in the oxygen affinity, the Bohr effect and the heme-heme interaction of Hb A (alpha 2 beta 2A) and Hb B (alpha 2 beta 2B), each containing one of the three possible alpha chain phenotypes.

Animals↗
PubMed1981

Evidence for multiple differing cation binding sites on hemoglobin A and S.

Some divalent cations (at 10(-3)M concentration) have been shown to act as oxygen-linked ligands. The effect of Ca++ (only on hemoglobin S) and Zn++ (on normal hemoglobin and hemoglobin S) can be traced to a preferential binding of these cations to the oxy- conformation of the proteins; the reverse is true for Ni++, since its presence reduces the oxygen affinity of both hemoglobins. The results suggest: i) the existence of at least two different cation binding sites on hemoglobin; ii) the replacement of glutamic acid by valine in hemoglobins S introduces sufficient structural modification to form a new cation binding site.

Binding Sites↗
PubMed1980

Renaturation and urea-induced denaturation of 20 beta-hydroxysteroid dehydrogenase studied in solution and in the immobilized state.

Tetrameric 20 beta-hydroxysteroid dehydrogenase (17,20 beta,21-trihydroxysteroid:NAD+ oxidoreductase, EC 1.1.1.53) from Streptomyces hydrogenans was reactivated after inactivation, dissociation and denaturation with urea. The effect of several factors such as NAD+, NADH, substrate, sulphydryl reducing agents, extraneous proteins, pH and enzyme concentration on reactivation was investigated. The coenzymes were found to be essential for obtaining a high reactivation yield (about 90%), since in their absence the reactivation was less than 10%. NADH was effective at lower concentrations than NAD+. The reactivated enzyme, after the removal of inactive aggregates, showed physical and catalytic properties coincident with those of the native enzyme. The mechanism by which NADH affects the reconstitution of 20 beta-hydroxysteroid dehydrogenase was investigated using both soluble enzyme and enzyme immobilized on Sepharose 4B. The immobilization demonstrates that isolated subunits are inactive and incapable of binding NADH and suggests that subunit association to the tetramer is essential for enzymatic activity. NADH appears to act, after subunit assembly has taken place, by stabilizing tetramers and preventing their aggregation with monomers that would give rise to inactive polymers.

20-Hydroxysteroid Dehydrogenases↗
PubMed1980

The reaction of hemoglobin Zürich with oxygen and carbon monoxide.

The present paper reports a spectroscopic and kinetic study of the reaction with oxygen and carbon monoxide of (a) the abnormal hemoglobin Zürich (beta 63, E7 His leads to Arg), (b) its isolated abnormal chains (beta ZH), and (c) a reconstituted hybrid containing cobalt instead of iron on the normal alpha chains (Co alpha)2-(Fe beta ZH)2. The abnormal beta ZH chains, isolated from hemoglobin Zürich (HbZH) tetramer, display very peculiar spectral properties in the Soret region which were determined, for the oxy and deoxy derivatives, by kinetic difference spectra. The spectral properties of abnormal chains are maintained in the native and reconstituted hybrid tetramer. The rate constants for CO and O2 binding to isolated beta ZH chains were compared with those of the normal alpha and beta chains, It is confirmed that the CO combination rate constant to beta ZH is much higher than that of normal chains, whereas that for O2 is similar for the normal and abnormal chains. The CO binding rate constant for Fe beta ZH chains in the hybrid tetramer is the same as in the native HbZH molecule, i.e. much higher than that of normal chain. The new data are fully consistent with the sequential mechanism for CO binding previously proposed by us; on the other hand, on the basis of the spectral and kinetic results, and contrary to what has been suggested by other authors, a sequential binding of the ligand is excluded in the case of O2.

Carbon Monoxide↗
PubMed1980

Luminescence of carbon monoxide hemocyanins.

The effect of carbon monoxide on the luminescence properties of Helix pomatia alpha-hemocyanin and Panulirus interruptus hemocyanin has been studied. These proteins, when saturated with carbon monoxide, show, besides the intrinsic fluorescence arising from the aromatic amino acid residues, emission in the visible region with a maximum between 540 and 560 nm. Results of carbon monoxide titration experiments and data from absorption and excitation-emission spectra provide convincing evidence that the observed emission originates from a fluorescent copper(I)-carbon monoxide complex, and this emission is interpreted as charge-transfer luminescence.

Animals↗