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F Ascoli

Publications and source records attributed to F Ascoli.

At least 109 records · Page 6Linked to original sources
PubMed1983

A circular dichroism study of the proton-linked transition in the carbomonoxy derivative of the hemoglobin component IV from trout.

Near ultraviolet and visible circular dichroism spectra of the carbomonoxy derivative of the hemoglobin component IV from trout Salmo irideus are pH-dependent in the range 6.2-7.8, and are affected by the presence of inositol hexaphosphate at pH 6.2. On the basis of previous studies, the spectral changes observed can be associated to the pH-dependent R4 leads to T4 transition occurring in the liganded protein. The CD spectra above 500 nm at low pH can be interpreted as due to release of the heme asymmetry in the T liganded conformation, in agreement with the movement of the iron toward the proximal histidine.

Allosteric Regulation↗
PubMed1983

Heterogeneity of the basic pancreatic inhibitor (Kunitz) in various bovine organs.

Four protein protease inhibitors (I, II, III, IV) having low molecular weights (10 600-6500) and basic isoelectric points were isolated by affinity chromatography from bovine spleen. Inhibitor IV was identified as the basic pancreatic trypsin inhibitor (Kunitz inhibitor); the presence and distribution of components I, II and III vary in the different bovine organs. Spleen inhibitors I, II, III and IV were purified by ion-exchange chromatography; they form 1:1 complexes with trypsin and inhibit enzymatic activity of trypsin, chymotrypsin and kallikrein. Inhibitors I, II and III contain carbohydrate moieties (7-4%) covalently bound to the polypeptide chain. Specific basic pancreatic trypsin inhibitor antiserum has shown the complete identity between inhibitor IV and the basic pancreatic trypsin inhibitor, while partial cross-reactivity between the basic pancreatic trypsin inhibitor and inhibitors I, II and III can be seen from a double immunodiffusion test.

Animals↗
PubMed1982

Studies on Scapharca hemoglobins. Properties of the dimeric protein reconstituted with Fe- or Co-porphyrin.

A native globin from the dimeric hemoglobin, hemoglobin I, of the mollusc Scapharca inaequivalvis has been obtained with the acid-acetone method. The globin has a lower sedimentation coefficient than the native protein at neutral pH; its reconstitution product with natural heme has the same physicochemical and functional properties as the native protein. proto- and meso-cobalt hemoglobin I have been prepared and characterized. proto-Cobalt hemoglobin I binds oxygen reversibly with a lower affinity and a lower cooperativity than native hemoglobin I; thus, the changes in the functional properties brought about by substitution of iron with cobalt are similar to those observed in human hemoglobin A. The EPR spectra of deoxy-proto-cobalt hemoglobin I and of the photolysis product of oxy-meso-cobalt hemoglobin I indicate that two histidine residues are the apical heme ligands. The broad signal at g = 2.38 in deoxy-proto-cobalt hemoglobin I points to a constrained structure of the heme site in this derivative which results from a distorted coordination of the hindered proximal histidine. A similar structure has been proposed previously for the alpha chains in deoxy-cobalt hemoglobin A.

Apoproteins↗
PubMed1982

Circular-dichroism study of the interaction of aspartate-aminotransferase isoenzymes with a coenzyme analog.

The interaction between a coenzyme derivative, 4'-N-(2,4-dinitro-5-fluorophenyl)-pyridoxamine 5'-phosphate, and the apoenzyme of cytoplasmic and mitochondrial aspartate aminotransferase, was studied by circular dichroism. The specific complexes initially formed were characterized by their circular dichroic spectra. The spectra indicate that the complex is very probably the same for the two isoenzymes. In contrast the spectra recorded during further reaction, in agreement with previous results, monitor different reaction paths and characterize the irreversible labeling at the active site of the cytoplasmic enzyme and regeneration of pyridoxal 5'-phosphate in the mitochondrial enzyme. By following circular dichroic changes in the mitochondrial enzyme, initial kinetic characterization of the cleavage of 4'-N-(2,4-dinitro-5-fluorophenyl)-pyridoxamine 5'-phosphate to form pyridoxal 5'-phosphate at the active site, is provided.

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

Amphitrite ornata erythrocruorin. I. Structural properties and characterization of subunit interactions.

A high molecular weight erythrocruorin (Mr approx. 3 . 10(6)) is found in the vascular system of the marine terebellid worm Amphitrite ornata, while a low molecular weight hemoglobin is contained in the coelomic cells. Polyacrylamide gel electrophoresis indicates that Amphitrite erythrocruorin contains three different types of polypeptide chain, of molecular weight approx. 15,000, whereas the molecular weight per heme group is approx. 20,000. These data suggest that only two of three polypeptide chains may be associated with a heme group. The coelomic hemoglobin, which occurs as a monomer, has an apparent molecular weight of approx. 14,000. The circular dichroism spectra of Amphitrite erythrocruorin and of the coelomic protein reveal marked differences in the heme environment, while the alpha-helical contents are not very different (60% and 70%, respectively). Amphitrite erythrocruorin is unusual in its dissociation behavior. Divalent cations are required for maintaining the quaternary structure. In the pH range 7.75--8.5, when the Ca2+ concentration is reduced below 1 mM, the whole molecule (57 S) dissociates into a number of lower molecular weight species (25, 15, 10 and 3 S) which have been correlated with specific subunit structures by electron microscopy. Whole molecules and 25 S subunits are not in equilibrium with the lower molecular weight species and can be isolated from partially dissociated mixtures. In contrast, the lower molecular weight subunits are themselves in a state of rapid equilibrium which is sensitive to cations, protons and oxygen. Of special interest is the dimerization reaction of the 10 S subunits, which appears to be mediated by Ca2+ and conforms to the predictions of the Cann and Goad theory on ligand mediated equilibria. The dissociation of Amphitrite erythrocruorin is readily reversible when the Ca2+ concentration is increased. The subunits obtained at physiological (7.8) or slightly acid (6.5) pH completely reassemble into whole molecules. Reassembly, however, is only partial when dissociation occurs at high pH. The presence of stable intermediates, such as the 15 S species, may facilitate the reassociation process.

Amino Acids↗
PubMed1978

Studies on erythrocruorin. VII. Reconstitution of earthworm erythrocruorin from the apoprotein.

Apoerythrocruorin prepared from the giant respiratory hemoprotein of the earthworm (60 S, Mr = 3 X 10(-6)) is an electrophoretically homogeneous molecule which sediments as a single peak of low molecular weight (3.5 S) and has a lower alpha-helical content (approx. 30%) than the native protein. Titration of globin with ferric heme indicates the presence of different binding sites; however, after purification by ion exchange chromatography, the reconstitution product contains 1 haem/23 000 g of protein as the native molecule. Reconstituted ferric erythrocruorin is a low molecular weight hemichrome with the same optical and physicochemical properties of the hemichrome formed by natural ferric erythrocruorin. Reconstituted ferrous erythrocruorin reacquires the alpha-helical content and the quaternary structure of the native molecule. Reassociation into 10-S speices (1/12 of the whole molecules) is fast and easy, while that into whole molecules is slow and somewhat erratic. The functional properties of reconstituted ferrous erythrocruorin (oxygen affinity, cooperativity in oxygen binding, magnitude of Bohr effect) are very similar to those of the "stable" low cooperativity form of the undissociated protein.

Apoproteins↗
PubMed1978

Infrared stretching frequencies of CO in carbomonoxyhemoglobin from trout.

The infrared spectra of the carbomonoxy derivatives of the hemoglobin components I and IV from trout have been measured in the CO stretching frequency region using a high resolution infrared spectrometer. The CO stretching frequency of Hb I CO is very close to that of carbomonoxy human hemoglobin and is pH-independent. In contrast, the CO stretching frequency of Hb IV CO is higher and shows a small but significant pH dependence in the range 6.2-7.8. These results point to a decreased strength of the iron-CO bond in Hb IV CO at low pH, in agreement with the conclusions drawn from the reported difference spectra of Hb IV CO as a function of pH.

Animals↗
PubMed1978

Properties of trout hemoglobins reconstituted with unnatural hemes.

Native globins isolated from trout hemoglobin compoents I and IV have been reconstituted with proto-, meso-, and deuteroheme, and the spectral and functional properties of the reconstituted hemoglobins have been investigated. Equilibrium and kinetic studies allow the following conclusions. (a) The properties of the proto-reconstituted hemoglobins are very similar, or indistinguishable, from those of the native Hb's I and IV. (B) The CO binding kinetics for both proteins were found to be consistent with the equilibrium data: the overall association rate constant increases (and the autocatalytic character of the reaction decreases) in the order proto, meso, deutero. (c) A marked pH dependence of both ligand affinity and cooperativity is maintained in the reconstituted Hb's IV: at pH 6 the fractional saturation with oxygen in air (Root effect) is lower for proto- than for meso- and deutero-Hb IV. The results obtained, including partial photodissociation experiments at different pH values, can be considered, to a first approximation, consistent with the basic features of a simple two-states model.

Allosteric Regulation↗
PubMed1977

Physicochemical and functional properties of Perinereis cultrifera (Grübe) erythrocruorin.

Perinereis erythrocruorin has the following physicochemical properties: So20,w = 55S, corresponding to a molecular weight around 2.7-10(6); minimum molecular weight (on the basis of the heme content) 23 700 +/- 500; isoelectric point 5.1; alpha-helix content approximately 40%. At alkaline pH values in the oxygenated form the 55-S molecules dissociate into subunits with a weight average sedimentation coefficient of 3S, corresponding to a molecular weight approximately 35 000. Deoxygenation of partially dissociated samples promotes association of the 3-S subunits into a 9S component. The functional properties of Perinereis erythrocruorin are characterized by a low cooperativity in oxygen binding (n 1/2 = 1.5) at neutral pH. Cooperativity increases reversibly towards both the acid and alkaline pH range, irrespective of changes in molecular weight. This finding, taken together with the ultracentrifuge results, suggests that a subunit may represent the functional unit of the protein. The pH dependence of the oxygen affinity can be accounted for in terms of a single oxygen linked group with a pK of 8.

Allosteric Site↗