Biomedical subjects

F Barceló

Publications and source records attributed to F Barceló.

30 records · Page 2Linked to original sources

PubMed1994

Calorimetric and spectroscopic studies on the poly[d(GA).d(CT)] structural polymorphism induced by zinc.

The interaction of zinc (II) with poly[d(GA).d(CT)] and salmon testes DNA has been investigated by Differential Scanning Calorimetry (DSC) and Circular Dichroism (CD). We have detected and energetically characterized the existence of two different structural forms in poly[d(GA).d(CT)] which behave differently during a DSC experiment. The overall melting of DNA shows two calorimetric transitions at different temperatures. Moreover, the presence of zinc, at an input ratio of ion to nucleotide (r) above two, renders a complex DSC profile which is characterized by a negative enthalpy transition. Besides, the low-temperature transition observed in the presence of zinc is practically reversible after re-cooling/re-heating cycles. Nevertheless, the high-temperature transition characterized by a negative delta H degree cal does not appear in re-heating experiments, and remains stable below 100 degrees C. A calorimetric negative enthalpy transition is also found using salmon DNA in the presence of zinc ions. It seems that the combination of a temperature effect and zinc binding might induce the production of a stable metal-DNA complex, which can also be detected by changes in some bands in the CD profiles. The experimental results show that the presence of DNA structures and binding processes involving a negative calorimetric enthalpy contribution might be more widespread than previously reckoned.

Animals↗

PubMed1993

Berenil recognizes and changes the characteristics of adenine and thymine polynucleotide structures.

Using circular dichroism, differential scanning calorimetry and susceptibility to DNAse I cleavage assays, we show that the interaction of berenil, a minor-groove binding drug, with poly(dA-dT).poly(dA-dT) and poly(dA).poly(dT) involves important changes in the polynucleotide conformation. The effect of berenil on poly(dA-dT).poly(dA-dT) comprises a clear alteration in CD spectra even at drug/DNA ratios smaller than the stoichiometric value. Berenil recognizes and binds to the alternating-B conformation of DNA changing it to a new conformation which appears to show some of the peculiarities of poly(dA).poly(dT), possibly through a modification in the helical parameters at the TpA and ApT steps. Such alteration is accompanied by a small calorimetric enthalpy change. Moreover, the calorimetric enthalpy does not change significantly whatever the input ratio of drug to poly(dA-dT).poly(dA-dT), indicating that berenil binding does not substantially alters the enthalpy of transition. In addition to increasing the melting temperature of the polynucleotide, berenil reduces the cooperativity of the poly(dA-dT).poly(dA-dT) transition slightly more than either distamycin or netropsin.

Binding Sites↗

PubMed1991

Equilibrium binding of four anthracyclines to nucleic acids: thermodynamic properties and sequence selectivity.

The thermodynamic parameters of the interaction of the two anthracyclines 13-dihydrodaunomycin and marcellomycin with calf thymus DNA were examined by equilibrium binding studies. Enthalpy and entropy changes of the binding of both drugs show salt dependence profiles that cannot be rationalized by the polyelectrolyte theory. This feature is common to other anthracycline compounds. The nucleotide sequence binding preferences of daunomycin, adriamycin, 13-dihydrodaunomycin and marcellomycin have been studied by monitoring the degree of protection from cleavage by restriction endonucleases of linearized pBR322. Differential protection of pBR322 DNA against the cleavage of Bgl I and Ava II suggests that these drugs recognize changes in the sequences near the enzyme recognition site. Alterations of the electrophoretic restriction pattern of pBR322 in the presence of anthracyclines are dependent on time and on concentration. These results are discussed in relation to the existence of nucleotide sequences with different affinity for these drugs.

Antibiotics, Antineoplastic↗

PubMed1991

Kinetics of the DNA binding of 2-substituted anthraquinones.

The DNA-binding properties of the 2-substituted-1,4-dihydroxyanthraquinones 5-12 were examined. Compounds 5 and 6 were synthesized in this study, 7-12 were already available. Spectral studies were consistent with intercalation of 5, 6 and 8 into DNA. Affinity constants were in the range of 3 x 10(4)M-1. Compounds 7 and 10-12 showed no DNA binding, presumably being sterically excluded from binding. The kinetics of the DNA interaction of 5, 6 and 8 were studied. There is a biphasic process. This may reflect an initial reaction, with drug from this first mode of binding moving into the second binding mode (a sequential process) or independent binding of drug in two sets of sites (a parallel process). The methods used in this study do not allow us to discriminate between these models. However, if the parallel binding model is correct, the compounds show sequence selectivity of binding, and provide a lead for further development of neutral DNA-binding ligands with sequence selectivity.

Anthraquinones↗

PubMed1990

A scanning calorimetric study of natural DNA and antitumoral anthracycline antibiotic-DNA complexes.

Thermal denaturation of natural DNA in the absence and presence of antitumor anthracycline antibiotics has been studied by adiabatic differential scanning calorimetry. The helix-coil transition is operationally irreversible as measured by DSC. Both the melting temperature and the overall molar transition enthalpy of the DNA samples was dependent on the percentage of GC base pairs. Calorimetric traces of anthracycline-DNA complexes have qualitatively similar features and the significance of this characteristic is discussed. The unsaturated drug-DNA complex melts through complex thermal transitions with one broad endotherm in the same temperature region as free DNA and the other at a higher temperature which is rf (mol ligand per mol DNA in base pairs) value dependent. Antibiotic binding at concentrations close to saturating conditions (rf = 0.2) reverts the melting range to a value near to its original one and increases the thermal stability of the duplex structure by around 30 degrees C. In addition, the calorimetric enthalpy is increased by between 64% and 150%, depending on which ligand was used.

Animals↗

PubMed1980

[alpha-n-benzoylarginine-2-naphthylamide-amidohydrolase activity in chicken liver (author's transl)].

The enzyme activity from chicken liver that hydrolizes alpha-N-benzoil-DL-arginine-2-naphthylamide (BANA) has been separated into three active fractions by chromatography on Sephadex G-100 and DEAE-cellulose. The enzyme in Fraction FEA has a molecular weight greater than or equal to 100,000. The other two enzymes in Fractions FE1B and FE2B have a molecular weight around 23,000 and are separated by DEAE-cellulose chromatography. The BANA-hydrolase of fraction FE2B is unstable at pH alkaline and activates trypsinogen, in contrast with the enzyme of fraction FEB1. Both are thiol enzymes which behave analogously against activators (cysteine, dithiotreitol and 2-mercaptoethanol) and inhibitors (PCMB, IAA, N-ethylmaleimide, Cu2+, Hg2+ and Zn2+).

Aminopeptidases↗

PubMed1980

[Acid proteinase of chicken liver. Purification and properties (author's transl)].

A method for purifying the haemoglobinolitic activity to acid pH in chicken liver is described. The purified preparation contains cathespin D activity since it is inhibited by diazoacetyl-DL-norleucine methylester in the presence of cupric ions, while thiol-enzyme reagents do not affect it. The molecular weight of the enzyme is approximately 40,000--45,000 and the pH optimum against haemoglobin and bovine serum albumin is 3.5-3.7. The rate of degradation of albumin and casein is much less than that of haemoglobin. Cathepsin D preparations with different purification degrees, exhibit a similar percentage of activation at acid pH; the highest activation is observed at pH 3.1-3.3.

Animals↗

PubMed1980

[Acid proteases from chicken liver. Cooperative hydrolysis of proteins (author's transl)].

Purified preparations of cathepsin D, BANA-hydrolase activity and dipeptidil aminopeptidase I from chicken liver, show a cooperative effect in the protein hydrolysis (acid-denatured haemoglobin and bovine serum albumin and native bovine serum albumin) at pH 5.0. The nature of the protein substrates determines their sensitivity to enzymatic digestion. The action of cathepsin D on proteins, in contrast which the BANA-hydrolase activity, releases polypeptides with high molecular weight, with scant--NH2 groups which can be valued by the ninhydrin method. These peptide fragments can then be further degraded by the protease BANA-hydrolase and the dipeptidil aminopeptidase I which is not active towards intact proteins.

Animals↗

PubMed1980

[Purification and properties of dipeptidyl amino-peptidase I from chicken liver (author's transl)].

Dipeptidyl aminopeptidase I (E.S. 3.4.14.1) from chicken liver was purified by the following steps: homogenization at pH 5, thermic precipitation, acetone fractionation and Sephadex G-100, DEAE-cellulose and organomercurial-Sepharose column fractionations. The purified enzyme appears to be homogeneous by polyacrylamide gel electrophoresis at both pH 4.5 and 8.3 and has an isoelectric point of 5.7 +/- 0.05. The molecular weight of the enzyme reale 167,000 +/- 17,000 on the Sephadex G-150 column chromatography. The optimum pH for hydrolysis of Gly-Phe-p-nitroanilide (GPNA) and Gly-Phe-B-naphthylamide was 5.8. The value of Km for the hydrolysis of GPNA was estimated at 3.3 mM. The enzyme required halide ions for activity and was activated by thiol reagents (dithiothreitol, cysteine and 2-mercaptoethanol). Accordingly, DAP I was inhibited by thiol-blocking reagents (PCMB, IAA, Hg2+). The enzyme oxidation with oxygen current was fostered by chloride anion (50 nM); nevertheless the activity was recovered when cysteine was present in the incubation mixture; the latter, besides, seems to perform as enzyme protector.

Animals↗

PubMedDate not supplied

[A critical review of the specificity of the Wisconsin card sorting test for the assessment of prefrontal function].

INTRODUCTION AND OBJECTIVE: Clinical and experimental research with the Wisconsin Card Sorting Test (WCST) has shown inconsistencies which bring into question the specificity of the test as a marker of frontal dysfunction. The aim of the present review is to evaluate the causes and the consequences of those criticisms for the assessment of both prefrontal function and the executive system of attention. DEVELOPMENT: Clinical evidence confirms that, in its present form, the WCST can not discriminate between lesions in frontal and non frontal brain regions. Moreover, functional neuroimaging studies have shown rapid and widespread activation of frontal and non frontal brain regions during WCST performance. On the one hand, these studies strongly suggest that the concept of anatomically 'pure' tasks is deceptive, but they also provide us with evidence that inconsistencies in WCST research might be motivated by problems with the internal validity and reliability of the original test as a measure of attentional set shifting ability. In contrast, recent studies have successfully employed WCST analogues to link precise cognitive processes with anatomically and functionally well defined prefrontal areas. CONCLUSIONS: It is deemed necessary to apply the new technical and methodological developments to generate more valid and reliable neuropsychological tests, that yield a better correspondence between anatomy and function. This will make possible future progress in the clinical assessment of higher brain functions.

Attention↗

PubMedDate not supplied

[Madrid adaptation of the Wisconsin card sorting test: a comparative study of internal consistency].

INTRODUCTION: WCST (Wisconsin Card Sorting Test) is still a widely used neuropsychological test for evaluation of disorders of the frontal lobes. Recent studies have cast doubt on the validity of WCST as a marker for frontal dysfunction. OBJECTIVES: We present a simplified version of WCST specially designed to evaluate the capacity to change the criteria for attention. Our objectives were to examine the difference in standards and in internal consistency between our adaptation and the conventional WCST. SUBJECTS AND METHODS: The two tests were applied to a group of 60 young persons with no cerebral disorders. The principal components of both tests were analysed for determine their internal structure. RESULTS: We found statistically significant differences between the scores of Spanish persons and the standard data for WCST. Analysis of the main components showed a solution of two components in the conventional WCST and a solution of three components in our adaptation. CONCLUSIONS: The American rating system underestimated the level of performance in the Spanish sample. Analysis of the internal consistency showed the excessively redundant and simple factorial structure of the conventional WCST. Our adaptation was shown to have a richer internal structure, with the order of error scores more in accord with the type of cognitive process involved. These advantages may be attributed to more exact analysis of non perseverant errors, subclassified as efficient errors (i.e. linked to comparison of hypotheses) and random errors (i.e. linked to loss of criteria for attention).

Adolescent↗

PubMedDate not supplied

[Electrophysiology of executive functions].

INTRODUCTION: In neuropsychology, executive functions have been defined as those that coordinate the flow of information processing in the brain. In the last decade its study has undergone an important development, partly due to the use of functional neuroimaging. DEVELOPMENT: Electrophysiological techniques have also provided a link between two specific components of the event related brain potential (ERP) and certain control and monitoring processes, as those described in theoretical frameworks of executive functioning (i.e., Norman & Shallice). On the one hand, attentional set shifting paradigms allow us to relate the anteriorly (P3a; latency 300-350 ms) and posteriorly (P3b; latency 450-600 ms) distributed components of the so called 'novelty P3', with a more general mechanism of attentional set shifting that could account for both stimulus and task novelty. On the other hand, 'error related negativity' (ERN or En) has shown its sensitivity to action monitoring (i.e., error detection and error correction processes), during the execution of response selection RT tasks. CONCLUSIONS: The comprehension of these two executive processes represents critical aspects in our understanding of brain function, and has direct applications to the design of both theoretical models and assessment and rehabilitation programs for patients with dysexecutive disorders.

Cognition↗