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Biomedical subjects

J Donoso

Publications and source records attributed to J Donoso.

At least 19 recordsLinked to original sources
PubMed2003

FT-IR study of pyridoxamine 5' phosphate.

Aqueous solutions of pyridoxamine 5' phosphate (PMP) at several pH conditions have been studied using FT-IR spectroscopy using the attenuated total reflection (ATR) technique. In spite of the strong intense OH stretching and bending bands of water, most of the vibrational structure of solute can be observed from 900 to 1500 cm(-1). With increasing pH, very intense changes in the spectra have been observed due to concentration changes of the hydrogen bonded species. Spectra of the different ionic species have been calculated from the mathematical fitting of experimental absorption spectra as a function of pH. Spectra are characterized by the presence of broad band-like structures in the 2400-3500 cm(-1) region, with extended continua that indicate very large proton polarizability of hydrogen bonds. Contributions of the phosphate group to the total absorption have been analyzed by comparison with pyridoxamine spectra.

Hydrogen-Ion Concentration↗
PubMed2001

Electrostatic and structural similarity of classical and non-classical lactam compounds.

Various electrostatic and structural parameters for a series of classical and non-classical beta-lactams were determined and compared in order to ascertain whether some specific beta-lactams possess antibacterial or beta-lactamase inhibitory properties. The electrostatic parameters obtained, based on the Distributed Multipole Analysis (DMA) of high-quality wavefunctions for the studied structures, suggest that some non-classical beta-lactams effectively inhibit the action of beta-lactamases. As shown in this work, such electrostatic parameters provide much more reliable information about the antibacterial and inhibitory properties of beta-lactams than do structural parameters.

Anti-Bacterial Agents↗
PubMed1998

[Treatment of hyperthyroidism].

The pathogenic mechanisms of Basedow Graves disease are not well known. Therefore there is not a unique therapy for it. It occurs at any age, but is most frequently seen in women from 20 to 50 years old. Three types of treatments are currently used. Antithyroid drugs efficiently abate initial symptoms, but relapses are frequent after discontinuing the therapy. Approximately 2% of patients have complications with the use of propylthiouracil. The second therapy is radioiodine that, in adequate doses, causes a partial or complete destruction of the gland. Most patients will require lifelong substitution therapy with thyroid hormones. When radioiodine cannot be used, surgical excision of the gland is the third form of therapy. There are also surgical complications and a high number of patients will also require substitution therapy. Choice of the type of treatment will depend on age of the patient, severity of the disease and other conditions, but the physician must discuss the choices with the patient.

Graves Disease↗
PubMed1994

Alkaline hydrolysis of cefotaxime. A HPLC and 1H NMR study.

A kinetic study on the alkaline hydrolysis of cefotaxime at pH 10.5 and 37 degrees C has been carried out by using HPLC and 1H NMR. The main resulting degradation products have been isolated and identified. These include, apart from the well-known deacetylcefotaxime, the exocyclic methylene derivative, the 7-epimer of cefotaxime and the 7-epimer of deacetylcefotaxime. The kinetic constants involved in the process have been determined and according to the experimental results the attack of the hydroxyl group on the ester function bonded to the 3'-carbon is the fastest step in the proposed kinetic scheme. It should be emphasized that the base-catalyzed epimerization of the hydrogen at the 7 position clearly depends on the presence of a good electron-withdrawing group at C(3'). On the other hand, no hydrolysis of the amide at position 7 was detected.

Cefotaxime↗
PubMed1994

Photophysical study of the Schiff bases of 5'-deoxypyridoxal and n-hexylamine in cationic micelles.

The absorption and fluorescence spectra of the Schiff bases formed between 5'-deoxypyridoxal and n-hexylamine in aqueous media containing different concentrations of the cationic surfactant hexadecyltrimethylammonium bromide were recorded at 25 degrees C. The quantum yields of fluorescence of the different zwitterionic and enol forms of the chemical species of the Schiff bases occurring in media of pH 4.5-8.5 were determined. Also, the fluorescence quenching resulting from the presence of the surfactant and that of iodide ion were analyzed. From the results obtained it follows that the zwitterionic forms do not interact with the cationic surfactant, whereas the enol forms do interact with it.

Amines↗
PubMed1993

Quantitative description of the absorption spectra of the coenzyme in glycogen phosphorylases based on log-normal distribution curves.

The absorption spectra of the coenzyme [pyridoxal 5'-phosphate (PLP)] in glycogen phosphorylase a (GPha), glycogen phosphorylase b (GPhb) and of the latter bound to various effectors and substrates were analysed on the basis of log-normal distribution curves. The results obtained showed that the ionization state of the PLP and GPha environment differs from that of GPhb. This divergence was interpreted in terms of tautomeric equilibria between some forms of the Schiff base of PLP and enzymic Lys-679. The ionic forms are slightly more predominant in GPha than they are in GPhb, so ionic and/or hydrogen-bonding interactions between the aromatic ring of PLP and GPha must be stronger than with GPhb. This confirms the purely structural role of the aromatic ring of the coenzyme. Binding of GPhb to AMP and Mg2+ results in the coenzyme adopting a similar state as in GPha. On the other hand, binding to IMP gives rise to no detectable changes in the tautomeric equilibrium of the coenzyme.

Animals↗
PubMed1992

[Persistent microalbuminuria in insulin-dependent diabetics and cardiovascular risk factors].

A possible association of cardiovascular risk factors and early diabetic nephropathy was investigated in 32 patients. Microalbuminuria (radioimmunoassay), total and HDL cholesterol and triglycerides (enzymatic methods), glycosylated hemoglobin (colorimetric methods), Apo A1 and B (immunonephelometric) and LDL were measured. Microalbuminuria was present in 28% of patients. Compared to subjects with no microalbuminuria they had increased levels of cholesterol (200.2 +/- 13.5 (SE) vs 168.6 +/- 9.4 mg/dl, p < 0.025) and LDL cholesterol (171.9 +/- 14.1 vs 137.4 +/- 9.1 mg/dl, p < 0.025). Systolic blood pressure was also higher in patients with microalbuminuria (127.8 +/- 3.9 vs 114.5 +/- 2.8 mmHg, p < 0.01). Microalbuminuria was correlated to the level of diastolic blood pressure (r = 0.74, p < 0.025). Thus, persistent microalbuminuria in insulin dependent diabetic patients is associated to cardiovascular risk factors which may explain the increased cardiovascular morbidity and mortality in these patients.

Adolescent↗
PubMed1991

Spectroscopic study of the Schiff bases of dodecylamine with pyridoxal 5'-phosphate and 5'-deoxypyridoxal. A model for the Schiff bases of pyridoxal 5'-phosphate in biological systems.

We recorded the absorption spectra of the Schiff bases of pyridoxal 5'-phosphate (PLP) and 5'-deoxypyridoxal (DPL) with dodecylamine (DOD) at different pH values. By applying deconvolution techniques to the spectra and analysing their different components we found that the above-mentioned Schiff bases in aqueous solutions of pH 7 adopted a conformation in which the pyridine ring is embedded in a very hydrophobic medium from which water is virtually completely excluded. This conformation in the same as that adopted by PLP when it acts as coenzyme for some enzymes such as glycogen phosphorylase. The experimental results obtained also show such a conformation to be highly favoured but sensitive to the protonation of the pyridine nitrogen, which makes the aromatic ring more readily accessible to the solvent.

Amines↗
PubMed1991

[Cushing's syndrome due to bilateral adrenal macronodular hyperplasia. From ACTH-dependent hypercortisolism to ACTH-independent hypercortisolism].

A 35 year old female with Cushing's syndrome and bilateral adrenal macronodular hyperplasia, in whom a change from ACTH dependency to autonomy was observed, is presented. The diagnosis of Cushing's syndrome was based on the failure of suppression of urinary ketogenic steroids (17 KCS) and free cortisol (uF) with the administration of 2 mg of dexamethasone daily for 2 days. CT scan of the abdomen showed adrenal bilateral multinodular hyperplasia and the sellar CT scan was normal. Initially 8 mg for 2 days of dexamethasone suppressed 17 KCS and uF; however, a few months later this effect was lost as well as the effect of endogenous ACTH on cortisol. Bilateral adrenalectomy was carried out, prior to attainment of normal cortisol levels with Ketoconazole. The adrenal glands has multiple nodules and they weighed 10 and 21 grams. Her postoperative plasmatic cortisol levels were imperceptible. Physiopathologic mechanisms involved in bilateral macronodular adrenal hyperplasia are reviewed.

Adrenal Glands↗
PubMed1989

[Tuberculosis and diabetes mellitus: a longitudinal-retrospective study in a teaching hospital].

We analyzed 1529 diabetic patients seen between 1959 and 1982 at a teaching hospital in Concepción, Chile. 116 of them were insulin dependent diabetics. Gestational diabetes was excluded. The 10 year actuarial risk of acquiring tuberculosis was 24.2% for insulin-dependent diabetics and 4.8% for the rest (p less than 0.001). The risk of the diabetic population as a whole was 5.9% compared to 0.8% for the population at large. Thus, diabetics are a high risk group for tuberculosis, especially insulin-dependent patients whose risk is about 38 times higher than the general population under 40 years of age.

Actuarial Analysis↗
PubMed1986

Study of the hydrolysis and ionization constants of Schiff base from pyridoxal 5'-phosphate and n-hexylamine in partially aqueous solvents. An application to phosphorylase b.

Formation and hydrolysis rate constants as well as equilibrium constants of the Schiff base derived from pyridoxal 5'-phosphate and n-hexylamine were determined between pH 3.5 and 7.5 in ethanol/water mixtures (3:17, v/v, and 49:1, v/v). The results indicate that solvent polarity scarcely alters the values of these constants but that they are dependent on the pH. Spectrophotometric titration of this Schiff base was also carried out. We found that a pKa value of 6.1, attributed in high-polarity media to protonation of the pyridine nitrogen atom, is independent of solvent polarity, whereas the pKa of the monoprotonated form of the imine falls from 12.5 in ethanol/water (3:17) to 11.3 in ethanol/water (49:1). Fitting of the experimental results for the hydrolysis to a theoretical model indicates the existence of a group with a pKa value of 6.1 that is crucial in the variation of kinetic constant of hydrolysis with pH. Studies of the reactivity of the coenzyme (pyridoxal 5'-phosphate) of glycogen phosphorylase b with hydroxylamine show that this reaction only occurs when the pH value of solution is below 6.5 and the hydrolysis of imine bond has started. We propose that the decrease in activity of phosphorylase b when the pH value is less than 6.2 must be caused by the cleavage of enzyme-coenzyme binding and that this may be related with protonation of the pyridine nitrogen atom of pyridoxal 5'-phosphate.

Amines↗
PubMed1984

Influence of pH on the removal of pyridoxal 5'-phosphate from phosphorylase b.

A method to break the pyridoxal 5'-phosphate (PLP)-phosphorylase b bond using hydroxylamine and slightly acid pH is put forward and described in the present paper. This method does not involve drastic conditions or deforming reagents. The influence of pH and protein concentration on the removal of PLP from phosphorylase has also been studied, resulting in an order of -0.3 with respect to the enzyme, a value that implies a complex reaction. An additional conclusion is that an increase in the protein concentration entails better protection of the enzyme from attack by hydroxylamine.

Animals↗
PubMed1983

Kinetic and thermodynamic study of the tetramerization equilibrium of phosphorylase b.

The association equilibrium of phosphorylase b, induced by AMP and in the presence of Mg2+, has been shown to be a reversible process that follows second order and first order reversible rate laws in the direction of tetramerization and dimerization respectively, this fact being independent of temperature and of enzyme and AMP concentrations. Moreover, rate and equilibrium constants have been evaluated and their dependence on temperature and AMP concentration studied in this work. An important role that the existence of two classes of AMP binding sites per enzymatic subunit plays in the aggregation properties of the enzyme has also been emphasized. In the presence of 0.1 and 1 mM AMP (binding to the high affinity site), the values of the change in enthalpy, activation energy of dimerization and activation energy of tetramerization are: -36 kcal/mol, +36 kcal/mol, and 0 kcal/mol respectively. Binding of AMP to the low affinity site (10 mM AMP) yields significant changes in the self-association equilibrium, since the preceding parameters reach the following values: -18, +32, and +14 kcal/mol.

Adenosine Monophosphate↗
PubMed1979

Sedimentation versus cytocentrifugation in the cytologic study of craniospinal fluid.

A sedimentation technique for cytologic study of CSF was compared with the standard cytocentrifugation method. Seventy-five samples from 37 children with leukemia and non-Hodgkin's lymphoma were processed by both methods. Total yield of cells and cytomorphology with differentials were analyzed. The techniques are comparable and both allow good cytologic study of the CSF even with very low cell counts/mm3. The sedimentation method can be used as an alternative, especially if a cytocentrifuge is not available. When both methods are used, the possibility of negative cell yield is decreased.

Centrifugation↗