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M Vásquez

Publications and source records attributed to M Vásquez.

At least 37 records · Page 2Linked to original sources
PubMed1991

On the multiple-minima problem in the conformational analysis of polypeptides. V. Application of the self-consistent electrostatic field and the electrostatically driven Monte Carlo methods to bovine pancreatic trypsin inhibitor.

In connection with the accompanying paper to test various models for the hydration of polypeptides, we have explored a limited portion of the conformational energy hyperspace of the small protein bovine pancreatic trypsin inhibitor (BPTI) with the aid of two search methods developed in this laboratory. A series of low-energy conformations was obtained as a result of this study. These conformations constitute a set of local minima in the conformational energy space of the molecule as described by the ECEPP/2 (Empirical Conformational Energy Program for Peptides) potential energy function, without the inclusion of hydration. Five different initial conformations were used in this exploration: the first corresponds to an energy-refined structure based on the crystallographic coordinates (4PTI) provided by Deisenhofer and Steigemann and reported previously by Meirovitch and Scheraga. The remaining four initial conformations were obtained by using a Variable-Target-Function procedure, applied to the experimental Cartesian coordinates (5PTI) reported by Wlodawer et al. The self-consistent electrostatic field (SCEF) and the electrostatically driven Monte Carlo (EDMC) methods were used to search the conformational space. The SCEF and EDMC methodologies assume that a polypeptide or protein molecule is driven toward the native structure mainly by the action of the electrostatic interactions. Application of these methodologies led to a set of conformations (up to 50 kcal/mol lower than the starting ones) with ECEPP/2 energies lower than any of those that we had previously found. Application of both methods to the initial conformation generated from 4PTI led to a series of low-energy conformations exhibiting similar rms deviations with respect to the experimental data (4PTI) as did the starting conformation. However, statistical analysis of the runs that had started from the conformations generated by using the variable-target-function procedure (and applying the EDMC method) indicated that the rms deviations of the atomic positions of the new low-energy conformations tended to increase as the energy improved, when compared with the X-ray data from which the starting conformations had been generated. The structures with the lowest energies also had radii of gyration smaller than the experimentally observed one. These results indicated a need to include hydration in the potential function, and provided the conformations used in the accompanying paper to test various hydration models.

Animals↗
PubMed1991

Empirical solvation models can be used to differentiate native from near-native conformations of bovine pancreatic trypsin inhibitor.

Several hydration models for peptides and proteins based on solvent accessible surface area have been proposed previously. We have evaluated some of these models as well as four new ones in the context of near-native conformations of a protein. In addition, we propose an empirical site-site distance-dependent correction that can be used in conjunction with any of these models. The set of near-native structures consisted of 39 conformations of bovine pancreatic trypsin inhibitor (BPTI) each of which was a local minimum of an empirical energy function (ECEPP) in the absence of solvent. Root-mean-square (rms) deviations from the crystallographically determined structure were in the following ranges: 1.06-1.94 A for all heavy atoms, 0.77-1.36 A for all backbone heavy atoms, 0.68-1.33 A for all alpha-carbon atoms, and 1.41-2.72 A for all side-chain heavy atoms. We have found that there is considerable variation among the solvent models when evaluated in terms of concordance between the solvation free energy and the rms deviations from the crystallographically determined conformation. The solvation model for which the best concordance (0.939) with the rms deviations of the C alpha atoms was found was derived from NMR coupling constants of peptides in water combined with an exponential site-site distance dependence of the potential of mean force. Our results indicate that solvation free energy parameters derived from nonpeptide free energies of hydration may not be transferrable to peptides. Parameters derived from peptide and protein data may be more applicable to conformational analysis of proteins. A general approach to derive parameters for free energy of hydration from ensemble-averaged properties of peptides in solution is described.

Animals↗
PubMed1991

Photoaffinity labeling of rotavirus VP1 with 8-azido-ATP: identification of the viral RNA polymerase.

Rotavirus single-shelled particles have several enzymatic activities that are involved with the synthesis of capped mRNAs both in vivo and in vitro. Because single-shelled particles must be structurally intact to carry out transcription, it has proven to be difficult to identify the protein within such particles that possesses associated RNA polymerase activity. One approach for characterizing the function of the individual proteins within single-shelled particles is to use nucleotide analogs to specifically label those proteins, such as the viral RNA polymerase, that have affinity for nucleotides. In this study, 8-azido-ATP (azido-ATP), a photoreactable nucleotide analog, was used to identify the viral RNA polymerase on the basis of the ability of the analog to inhibit transcription activity associated with rotavirus particles on exposure to UV light. When single-shelled particles were treated with UV light in the presence of [alpha-32P]azido-ATP, the structural protein VP1 became radiolabeled because of cross-linking of the nucleotide analog, and there was a corresponding decrease in the ability of the particles to synthesize mRNA. In parallel experiments in which single-shelled particles were not exposed to UV light, VP1 was not radiolabeled and the particles successfully used azido-ATP as a substrate for the synthesis of viral mRNAs. Taken together, these results are consistent only with the conclusion that VP1 is the rotavirus RNA-dependent RNA polymerase.

Adenosine Triphosphate↗
PubMed1991

Nutrition and education. II. Educational achievement and nutrient intake of Chilean elementary and high school graduates.

The interrelationships between educational achievement (EA) and nutrient intake were investigated in 550 Chilean adolescent schoolers graduating from elementary and high school. The random sample included schoolers from both educational levels (1:1), from public and private schools (1:1), and from high, medium, and low socioeconomic status (SES) (1:1:1). Standard procedures for 24-hour dietary recall interviews were used to collect data, and adequacy of intake was assessed by the FAO/WHO Pattern. EA was measured by means of the Achievement Evaluation Program (AEP) and Academic Aptitude Test (AAT) in elementary and high school, respectively. In elementary school graduates, results showed a significant and positive correlation between EA (AEP) and energy, protein, riboflavin, ascorbic acid, calcium and vitamin A intake (Multiple r = 0.456 p less than 0.01; r2 = 0.208). The School Feeding Program beneficiaries who belonged to the low SES presented the lowest EA (AEP) together with a deficient nutrient intake, especially for energy, riboflavin, niacin, vitamin A and calcium, at the same time that they registered the lowest values for those anthropometric parameters, indicators of past nutrition, that is to say height-for-age, weight-for-age, head circumference-for-age and a higher upper-to-lower segment ratio, as compared with non-beneficiaries from the same SES and with those from the higher strata. In high-school graduates, EA (AAT) was found to be significantly and positively correlated with protein, calcium, riboflavin and iron intake (Multiple r = 0.438 p less than 0.001; r2 = 0.192). Nevertheless, these interrelationship are strongly related to SES and sex. Results showed that educational achievement (EA) is significantly and positively associated with nutrient intake, this fact being important for educational planning related to the School Feeding Program.

Achievement↗
PubMed1991

[Sublingual captopril versus nifedipine in the treatment of hypertensive crisis].

The currently accepted drug of choice for treatment of hypertensive crisis is sublingual nifedipine. We compared the effects of sublingual captopril (25 mg) to those of nifedipine (10 mg) in 54 patients with this complication who came to the emergency room. Five min after administration of captopril, blood pressure decreased from 197.5 +/- 32.7/118.3 +/- 8.2 to 156 +/- 27.2/95.8 +/- 12.9 mmHg and heart rate decreased from 87.9 +/- 15.1 to 74.7 +/- 10.9 (p < 0.05). Blood pressure in the nifedipine group decreased from 198 +/- 27.3/120 +/- 9.8 to 147.7 +/- 17.8/86 +/- 17.9 (p < 0.05), while no change was observed in heart rate. Delayed measurements showed lower diastolic pressures at 60 and 75 min and lower systolic pressure at 120 min in the nifedipine group (p < 0.054). Few and not significantly different side effects were observed with both drugs. Thus, sublingual captopril is useful for treatment of hypertensive crisis.

Administration, Sublingual↗
PubMed1991

[Vibration and acoustic stimulation during labor with external monitoring. Pathology of fetal heart rate].

Vibratory acoustic stimulation was done in patients with an abnormal fetal heart rate tracing in external continuous electronic monitoring during labor, correlating with Apgar score, meconium staining and umbilical cord pH, describing a 83.3% sensitivity, 81.3% specificity and 62.5% positive predictive value. The authors recommend the use of vibratory acoustic stimulation in those cases with an abnormal fetal heart rate tracing in external continuous electronic monitoring, when we can not install internal electronic monitoring or obtain a fetal blood pH on assessment of fetal well-being.

Acoustic Stimulation↗
PubMed1990

Helix-coil stability constants for the naturally occurring amino acids in water. XXIII. Proline parameters from random poly (hydroxybutylglutamine-co-L-proline).

Water-soluble random copolymers containing L-proline and N5-(4-hydroxybutyl)-L-glutamine were synthesized by copolymerization of the tripeptides H-L-Glu(OBzl)-L-Glu(OBzl)-L-Glu(OBzl)-OH and H-L-Glu(OBzl)-L-Pro-L-Glu(OBzl)-OH, using benzotriazolyl-N-oxy-tris(dimethylamino)-phosphonium hexafluorophosphate as condensing reagent, and subsequent aminolysis of the Bzl ester groups with 4-amino-1-butanol. These copolymers were found to contain significant amounts of N5-(4-hydroxybutyl)-D-glutamine, thus requiring the synthesis of a binary copolymer containing only D- and L-N5-(4-hydroxybutyl)glutamine residues in order to evaluate the possible effects of the D-residues on the conformational properties of poly(hydroxybutylglutamine-co-L-proline). The different copolymers were fractionated, and their thermally induced helix-coil transition curves were obtained in water at neutral pH. When proper corrections were applied for the helix-destabilizing properties of N5-(4-hydroxybutyl)-D-glutamine, the Zimm-Bragg parameters sigma and s for L-proline could be deduced from the melting curves of poly(hydroxybutylglutamine-co-L-proline). The results indicate that L-proline acts as a very strong helix breaker over the entire temperature range from 0 to 60 degrees C.

Amino Acid Sequence↗
PubMed1989

High-resolution NMR studies of fibrinogen-like peptides in solution: structure of a thrombin-bound peptide corresponding to residues 7-16 of the A alpha chain of human fibrinogen.

The interaction of the following human fibrinogen-like peptides with bovine thrombin was studied by one- and two-dimensional NMR techniques in aqueous solution: acetyl-Phe(8)-Leu(9)-Ala(10)-Glu-(11)-Gly(12)-Gly(13)-Gly(14)-Val(15)-Ar g(16)- Gly(17)-Pro(18)-NHMe (F6), acetyl-Phe-Leu-Ala-Glu-Gly-Gly-Gly-Val-Arg(16) (tF6), acetyl-Asp(7)-Phe-Leu-Ala-Glu-Gly-Gly-Gly-Val-Arg(16)-Gly(17)-Pro- Arg(19)-Val(20)-NHMe (F8), and acetyl-Asp-Phe-Leu-Ala-Glu-Gly-Gly-Gly-Val-Arg(16) (tF8). At pH 5.3 and 25 degrees C, the Arg(16)-Gly(17) peptide bonds in both F6 and F8 were cleaved instantaneously in the presence of 0.5 mM thrombin, producing truncated peptides tF6 and tF8 and other peptide fragments. On the basis of observations of line broadening, thrombin was found to bind to the cleavage products, tF6 and tF8, of peptides F6 and F8. Peptide tF8 may have a higher affinity for thrombin than peptide tF6, as suggested by the more pronounced thrombin-induced line broadening on the proton resonances in peptide tF8. Transferred NOE (TRNOE) measurements were made of the complexes between thrombin and peptides tF6 and tF8. Medium- and long-range NOE interactions were found between the NH proton of Asp(7) and the C beta H protons of Ala(10), between the C alpha H proton of Glu(11) and the NH proton of Gly(13), and between the ring protons of Phe(8) and the C alpha H protons of Gly(14) and the C gamma H protons of Val(15). Sets of structures of the decapeptide tF8 were deduced by use of distance geometry calculations based on sequential and medium- and long-range TRNOEs from the thrombin-bound peptide. A predominant feature of these structures is the nonpolar cluster formed by the side chains of residues Phe(8), Leu(9), and Val(15) that are directly involved in binding to thrombin. This structural feature is brought about by an alpha-helical segment involving residues Phe(8)-Ala(10), followed by a multiple-turn structure involving residues Glu(11)-Val(15). These results provide an explanation for the observations that Asp(7), Phe(8), and Gly(12) are strongly conserved in mammalian fibrinogens and that the mutations of Asp(7) to Asn(7) and of Gly(12) to Val(12), result in delayed release of fibrinopeptide A, producing human bleeding disorders.

Amino Acid Sequence↗
PubMed1989

[Sweet lupine (Lupinus luteus, var. Aurea/Weico and Lupinus albus, var. Multolupa) proteins. I. Extraction and filtration by Sephadex].

Samples of Lupinus luteus, var. Aurea/Weico and Lupinus albus var. Multolupa flours were analyzed. The flour proteins were extracted and fractionated by gel filtration, and the per cent pattern for both globulins and albumins was then determined. The dehulled seeds, previously analyzed for composition, were ground, defatted and consecutively extracted with distilled water (pH 5.0) and phosphate buffer (0.05 M, pH 8.5). The extracted protein content was measured by the Lowry simplified method. Globulins (pH 8.5 fraction) from both species were filtered through Sephadex G-100; besides, Lupinus albus globulins were filtered through Sephadex G-150, and absorbance of the collected fractions was measured at 280 nm. The dehulled seed (DS) of L. luteus and L. albus revealed a good protein content (58.2 and 41.0%, respectively). The protein extracted from L. luteus was constituted by 17% albumins and 58.4% globulins. In contrast, L. albus presented a higher albumin content (55.6%) than globulins (31.5%). The elution pattern for the Sephadex G-200 gel filtration showed for both lupine species analyzed a preponderant peak I corresponding in L. luteus to 55.0% and in L. albus to 84.1% of the total globulins content. From these results, it may be concluded that the dehulled seed protein content is 42.0% higher for the L. luteus sample than for the L. albus. The applied methodology indicated a predominant content of globulins above albumins in L. luteus, while in the case of L. albus, the albumin content was the highest.

Albumins↗
PubMed1989

[Sweet lupine (Lupinus luteus, var. Aurea/Weico and Lupinus albus, var. Multolupa) proteins. II. Separation by electrophoresis].

The albumins and globulins extracted from Lupinus luteus var. Aurea/Weico and Lupinus albus var. Multolupa defatted flour samples were analyzed by polyacrilamide gel electrophoresis. The purpose was to determine the percentage distribution of pattern in the electrophoretograms and the relative mobility values of protein. The L. luteus albumins densitogram showed six fractions, two of them, No. 2 and No. 4, represented 58.1% of the total. On the other hand, the globulins densitogram revealed five fractions, numbers 1, 2 and 3 representing 90.7%. The densitogram of peak I from Sephadex G-100 globulins filtration indicated two fractions similar to those number 1 and 2 of the total globulins, showing low relative mobility values (from 0.26 to 0.39). The L. albus albumins resolved in four fractions, with No. 2 being the most prevalent (54.3%). In regard to the L. albus globulins, these showed five fractions identical in distribution with those of peak I, fraction 2 appearing as the most important (48.2%). It was found that Sephadex G-100 did not perform a good separation. As to the relative mobility values of globulins, fractions 2 and 3 were the most prominent (relative mobility of 0.35 and 0.48, respectively). It may be concluded that L. luteus albumins presented more components but with lower relative mobility values than those of L. albus. As for the globulins from both lupine flour samples, the gel separated fractions were classified in two groups of components, those of high and of low relative mobility.

Albumins↗
PubMed1988

Calculation of protein conformation by the build-up procedure. Application to bovine pancreatic trypsin inhibitor using limited simulated nuclear magnetic resonance data.

Low-energy conformations of a set of tetrapeptides derived from the small protein bovine pancreatic trypsin inhibitor (BPTI) were generated by a build-up procedure from the low-energy conformations of single amino acid residues. At each stage, various-size fragments were built up from all combinations of smaller ones, the total energies were then minimized, and the low-energy conformations were retained for the next stage. The energies of the tetrapeptides were re-ordered by including the effects of hydration. No information other than the amino acid sequence was used to obtain the low-energy conformations of the hydrated tetrapeptides. The latter were then supplemented with a limited set of simulated NMR distance information, derived from the X-ray structure of BPTI, to provide a basis for building the rest of the whole protein molecule by the same procedure. A total of 189 upper bounds, plus 12 pairs of upper and lower bounds pertaining to the location of the three disulfide bonds in this molecule, were used. Four sets of conformations of the entire molecule were generated by utilizing different combinations of smaller fragments. It was possible to obtain low-energy conformations with small rms deviations, 1.1 to 1.4 A for the alpha-carbons, from the structure derived by X-ray diffraction. The average deviations of the backbone dihedral angles were also low, viz. 23 degrees to 26 degrees.

Amino Acid Sequence↗
PubMed1988

Variable-target-function and build-up procedures for the calculation of protein conformation. Application to bovine pancreatic trypsin inhibitor using limited simulated nuclear magnetic resonance data.

An implementation of the variable-target-function procedure, first introduced by Braun and Go [W. Braun and N. Go, J. Mol. Biol. 186, 611-626 (1985)], has been used to generate conformations of the small protein bovine pancreatic trypsin inhibitor (BPTI), given a limited set of simulated data that could be obtained by nuclear magnetic resonance (NMR) techniques. A hybrid strategy was also used to calculate conformations of BPTI, given the same information. In the hybrid strategy, low-energy structures of medium-size fragments (decapeptides) of BPTI were generated using the variable-target-function method, followed by restrained energy optimization. The low-energy conformations were used as a basis to build up the complete fifty-eight-residue BPTI molecule. By using the variable-target-function approach, in which energy considerations were not introduced until full conformations of the entire BPTI molecule had been generated, it was not possible to obtain calculated structures with rms deviations from the X-ray conformation of less than 1.6 A for the alpha-carbons. On the other hand, with the hybrid strategy, which involved the consideration of realistic energy terms in the early stages of the calculations, it was possible to calculate low-energy conformations of BPTI with rms deviations from the X-ray structure of 1.06 to 1.50 A for the alpha-carbons. When the rms deviations were computed along the amino acid sequence, it was found that there was a good correlation between deviations among the calculated structures and deviations from the X-ray structure.

Aprotinin↗
PubMed1987

[Supplementation of wheat flour with chickpea (Cicer arietinum) flour. II. Chemical composition and biological quality of breads made with blends of the same].

Experimental bread made of wheat flour complemented with 5, 10 and 15% chick-pea flour was studied, using wheat bread as control. Samples were analyzed for their proximal chemical composition and amino acids content. Crude fiber and protein increased from 0.36% to 0.55%, and from 14% to 17.6%, respectively, when 15% chick-pea flour was added. The lysine content increased as the level of supplementation was raised. Biological quality of proteins was measured in rats as protein efficiency ratio (PER) as well as apparent digestibility resulting in an increase of PER values from 0.90 to 1.34 and small variations in bread protein digestibility. Bread nutritive value was significantly improved by adding chick-pea flour.

Amino Acids↗
PubMed1986

[Food habits of high school graduates in the metropolitan area of Santiago, Chile].

The purpose of this study was to determine the food habits of Chilean high-school graduates, and measure the effect that socioeconomic level (SEL), type of school (public and private school), sex and age exerts on those habits. A random and stratified sample of 283 schoolers, according to type of school, sex and SEL, measured through the Graffar Modified Scale was selected for the study. Food habits were defined by the frequency of consumption of food, expressed as days per week and were compared with the Model Allowance established by the Ministry of Health of Chile. A food habits questionnaire was administered to students by duly trained interviewers, and were defined by the frequency of consumption of food groups. Data were analyzed by the chi-square procedure, analysis of variance and Student's "t" test. In accordance with the results, the most consumed foods (over 90% of students) were meat, poultry, eggs, potatoes, apples, bread, rice, oil and butter or margarine. On the other hand, the most disliked foods (40% and more of students) were fresh cheese, viscera, radish and chickpeas. The high SEL students showed a significantly greater frequency of consumption of dairy products, and of meat products and eggs (p less than 0.001). No differences were found according to type of school, sex and age of students. We conclude, therefore, that SEL exerts a significant effect on food habits, in spite of which they were adequate according to the Model Allowance.

Adolescent↗