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C Salerno

Publications and source records attributed to C Salerno.

At least 73 records · Page 4Linked to original sources
PubMed1986

Interaction of lucensomycin with cholesterol in membranes: kinetic and structural studies.

The variations of optical density and fluorescence of lucensomycin are good indices of the binding of this polyenic antibiotic to membranes. The former parameter reflects more generally the binding to any site present in the membrane, while the latter is more specific for binding to cholesterol. Equilibrium titration experiments performed in the presence of an excess of membrane-bound cholesterol suggest that lucensomycin self-associates and that the binding and polymerization sites of the antibiotic are identical or quasi-identical; hence polymerization leads to a loss of binding sites and vice versa. The non-steroidal components of the membrane (such as proteins and lipids) seem to affect the rate of the individual reaction leading to the formation of the cholesterol-lucensomycin complexes, rather than the ratio among these heterologous aggregates at equilibrium. Polyene concentrations, which induce detectable proton release from unilamellar vesicles, are at least two orders of magnitude higher than those necessary to perform a spectroscopic titration of membrane cholesterol.

Antifungal Agents↗
PubMed1985

Hypoxanthine-guanine exchange by intact human erythrocytes.

The uptake and release of [14C]hypoxanthine by human erythrocytes, suspended in a tris(hydroxymethyl)aminomethane (Tris)-glucose-NaCl isotonic medium (pH 7.4), have been studied at 37 degrees C. The uptake of hypoxanthine, mediated by its incorporation into inosine 5'-monophosphate (IMP), was markedly stimulated by preincubating the cells in phosphate-buffered saline. After a lag time, [14C]IMP-enriched erythrocytes released [14C]hypoxanthine in the medium. Formycin B, at concentrations known to inhibit purine nucleoside phosphorylase in intact erythrocytes, affected hypoxanthine uptake and release and led to an increase in the intracellular concentration of inosine, suggesting that the main catabolic path of IMP is the sequential degradation of the nucleotide to inosine and hypoxanthine. The addition of guanine to a suspension of [14C]IMP-enriched erythrocytes led to an increase in the rate of [14C]hypoxanthine release, which was unaffected by the presence of formycin B. During the guanine-induced hypoxanthine release, guanine was taken up by the cells as GMP. These results suggest that the presence of guanine in the incubation medium activates a catabolic path in human erythrocytes leading to IMP degradation without formation of inosine.

Erythrocytes↗
PubMed1984

Kinetics of conformational changes in melittin. A circular-dichroic stopped-flow study.

The kinetics of the conformational changes undergone by melittin in aqueous solution upon interaction with ions and/or detergents were studied by following the variations of intrinsic ellipticity of the peptide with a circular-dichroic stopped-flow apparatus. The results were consistent with a simplified model in which salt induces a modification of the structure of melittin monomer, which may then aggregate into a polymeric assembly. Interaction with detergent micelles followed more complex kinetics.

Anions↗
PubMed1983

Adenine-induced hypoxanthine release from IMP-enriched human erythrocytes.

Adenine uptake and hypoxanthine release by IMP-enriched human erythrocytes has been studied. The presence of IMP within the erythrocytes leads to an increase in the rate of adenine incorporation. Adenine is taken up by IMP-enriched erythrocytes as AMP, even when intracellular 5-phosphoribosyl-1-pyrophosphate concentration is undetectable and too low to allow IMP synthesis from hypoxanthine. During adenine uptake and AMP synthesis, hypoxanthine is released by the cells. The possibility that 5-phosphoribosyl-1-pyrophosphate, necessary for AMP synthesis, is formed through the hypoxanthine guanine phosphoribosyltransferase-catalyzed IMP pyrophosphorolysis is considered.

Adenine↗
PubMed1982

A calorimetric study of the interaction of pyridoxal 5'-phosphate with aspartate apoaminotransferase and model compounds.

Schiff base formation between pyridoxal 5'-phosphate and model compounds of increasing complexity (i.e. L-valine and poly-L-lysine) and between pyridoxal 5'-phosphate and the apoenzyme of aspartate aminotransferase has been analyzed by microcalorimetric methods. The apparent pKa values and protonation enthalpy values for the relevant groups ionizing in the pH 4-9 range have been determined for the Schiff bases of L-valine and of poly-L-lysine. Upon Schiff base formation, the only noticeable change is the lowering of the ring nitrogen pK, accompanied by an increase of the relative delta H. In the poly-L-lysine Schiff base, however, the delta H relative to the protonation of the phosphate dianion becomes more negative. This behavior suggests a multiple interaction between the polymer and the ligand. The intrinsic heat of formation is small (congruent to -1 kcal/mol), of the same order of magnitude for both Schiff bases, and appears to be independent of the nature of the aminic reagent. The heat of reaction of pyridoxal 5'-phosphate with aspartate apoaminotransferase has been determined in the pH 6.2-8.8 range at 19 degrees C and at 25 degrees C. Each isotherm is characterized by a lack of proton evolution, a result that is unexpected on the basis of the known pK values of the reagents, and by a sharp pH dependence of the enthalpy change. Moreover, comparison of the two isotherms allows: (a) detection of a protonation-dependent effect (pK 7.5 at 25 degrees C), (b) exclusion of a preferential binding of the coenzyme to the apoenzyme in a particular ionization state; and (c) suggestion of a tightening of the protein molecule upon holoenzyme formation.

Animals↗
PubMed1982

Kinetics of coupled reactions catalyzed by aspartate aminotransferase and glutamate dehydrogenase.

Liver mitochondrial aspartate aminotransferase and glutamate dehydrogenase catalyze following sequence of reactions: see formula in text. In the presence of a slight excess of dehydrogenase, the time course of NADPH oxidation resulting from the overall reaction goes through a lag phase and reaches a linear phase. The slopes of the linear part of this curve is a linear function of transaminase concentration. At high concentration (approximately or equal to 10 microM) of both enzymes the lag phase, as observed after rapid mixing of the two enzymes in a Durrum stopped-flow spectrophotometer, is shorter, than that predicted from the kinetic parameters determined for the separate reactions catalyzed by each enzyme.

Animals↗
PubMed1981

Action of D-penicillamine on immunocomplexes containing rheumatoid factor.

The affinity between purified rheumatoid factors (RF) and native or heat aggregated human IgG has been studied in vitro by polarization fluorescence in the presence and in the absence of D-penicillamine. The value of the dissociation constant was the same using native and heat aggregated IgG suggesting that binding to the aggregated protein is not dependent on the exposure of a new determinant lacking in the native molecule. The results obtained in the presence of D-penicillamine suggest that the concentration of the drug necessary to get a pronounced effect on the apparent dissociation constant of the immunocomplex between IgG and RF is not reached in vivo, in clinical situations.

Antigen-Antibody Complex↗
PubMed1981

Human hypoxanthine guanine phosphoribosyltransferase. The role of magnesium ion in a phosphoribosylpyrophosphate-utilizing enzyme.

The role of Mg ions in the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction have been studied using accurate values of proton and Mg stability constants of phosphoribosylpyrophosphate (P-Rib-PP) determined from pH titration data. The results obtained favor the conclusion that the dimagnesium salt of P-Rib-PP is the true substrate of the enzyme. The other species of P-Rib-PP do not appreciably affect the initial reaction rate. The inhibition of the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction observed at high MgCl2 concentration can be attributed to a competitive inhibition of Mg2+ with respect to the dimagnesium salt of P-Rib-PP, suggesting that these ionic species bind to the same enzyme form. At a fixed [P-Rib-PPtot], the concentration of its dimagnesium complex is a sigmoidal function of MgCl2 concentration, suggesting that caution must be employed in the interpretation of sigmoidal saturation curves for P-Rib-PP-utilizing enzymes when low and not constant concentrations of the divalent cation are used.

Erythrocytes↗