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N Medina

Publications and source records attributed to N Medina.

At least 19 recordsLinked to original sources
PubMed2001

The complete genome of the crenarchaeon Sulfolobus solfataricus P2.

The genome of the crenarchaeon Sulfolobus solfataricus P2 contains 2,992,245 bp on a single chromosome and encodes 2,977 proteins and many RNAs. One-third of the encoded proteins have no detectable homologs in other sequenced genomes. Moreover, 40% appear to be archaeal-specific, and only 12% and 2.3% are shared exclusively with bacteria and eukarya, respectively. The genome shows a high level of plasticity with 200 diverse insertion sequence elements, many putative nonautonomous mobile elements, and evidence of integrase-mediated insertion events. There are also long clusters of regularly spaced tandem repeats. Different transfer systems are used for the uptake of inorganic and organic solutes, and a wealth of intracellular and extracellular proteases, sugar, and sulfur metabolizing enzymes are encoded, as well as enzymes of the central metabolic pathways and motility proteins. The major metabolic electron carrier is not NADH as in bacteria and eukarya but probably ferredoxin. The essential components required for DNA replication, DNA repair and recombination, the cell cycle, transcriptional initiation and translation, but not DNA folding, show a strong eukaryal character with many archaeal-specific features. The results illustrate major differences between crenarchaea and euryarchaea, especially for their DNA replication mechanism and cell cycle processes and their translational apparatus.

Cell Cycle Proteins↗
PubMed2001

The energetic cost of induced fit catalysis: Crystal structures of trypsinogen mutants with enhanced activity and inhibitor affinity.

The contribution of induced fit to enzyme specificity has been much debated, although with little experimental data. Here we probe the effect of induced fit on enzyme specificity using the trypsin(ogen) system. BPTI is known to induce trypsinogen to assume a trypsinlike conformation. Correlations are observed between BPTI affinity and the values of k(cat)/K(m) for the hydrolysis of two substrates by eight trypsin(ogen) variants. The slope of both correlations is -1.8. The crystal structures of the BPTI complexes of four variant trypsinogens were also solved. Three of these enzymes, K15A, DeltaI16V17/D194N, and DeltaI16V17/Q156K trypsinogen, are 10- to 100-fold more active than trypsinogen. The fourth variant, DeltaI16V17 trypsinogen, is the lone outlier in the correlations; its activity is lower than expected based on its affinity for BPTI. The S1 site and oxyanion hole, formed by segments 184A-194 and 216-223, are trypsinlike in all of the enzymes. These structural and kinetic data confirm that BPTI induces an active conformation in the trypsin(ogen) variants. Thus, changes in BPTI affinity monitor changes in the energetic cost of inducing a trypsinlike conformation. Although the S1 site and oxyanion hole are similar in all four variants, the N-terminal and autolysis loop (residues 142-152) segments have different interactions for each variant. These results indicate that zymogen activity is controlled by a simple conformational equilibrium between active and inactive conformations, and that the autolysis loop and N-terminal segments control this equilibrium. Together, these data illustrate that induced fit does not generally contribute to enzyme specificity.

Amino Acid Substitution↗
PubMed2000

Fine organization of Bombyx mori fibroin heavy chain gene.

The complete sequence of the Bombyx mori fibroin gene has been determined by means of combining a shotgun sequencing strategy with physical map-based sequencing procedures. It consists of two exons (67 and 15 750 bp, respectively) and one intron (971 bp). The fibroin coding sequence presents a spectacular organization, with a highly repetitive and G-rich (approximately 45%) core flanked by non-repetitive 5' and 3' ends. This repetitive core is composed of alternate arrays of 12 repetitive and 11 amorphous domains. The sequences of the amorphous domains are evolutionarily conserved and the repetitive domains differ from each other in length by a variety of tandem repeats of subdomains of approximately 208 bp which are reminiscent of the repetitive nucleosome organization. A typical composition of a subdomain is a cluster of repetitive units, Ua, followed by a cluster of units, Ub, (with a Ua:Ub ratio of 2:1) flanked by conserved boundary elements at the 3' end. Moreover some repeats are also perfectly conserved at the peptide level indicating that the evolutionary pressure is not identical along the sequence. A tentative model for the constitution and evolution of this unusual gene is discussed.

Animals↗
PubMed2000

Gene content and organization of a 281-kbp contig from the genome of the extremely thermophilic archaeon, Sulfolobus solfataricus P2.

The sequence of a 281-kbp contig from the crenarchaeote Sulfolobus solfataricus P2 was determined and analysed. Notable features in this region include 29 ribosomal protein genes, 12 tRNA genes (four of which contain archaeal-type introns), operons encoding enzymes of histidine biosynthesis, pyrimidine biosynthesis, and arginine biosynthesis, an ATPase operon, numerous genes for enzymes of lipopolysaccharide biosynthesis, and six insertion sequences. The content and organization of this contig are compared with sequences from crenarchaeotes, euryarchaeotes, bacteria, and eukaryotes.

Amino Acid Sequence↗
PubMed2000

A BAC library and paired-PCR approach to mapping and completing the genome sequence of Sulfolobus solfataricus P2.

The original strategy used in the Sulfolobus solfataricus genome project was to sequence non overlapping, or minimally overlapping, cosmid or lambda inserts without constructing a physical map. However, after only about two thirds of the genome sequence was completed, this approach became counter-productive because there was a high sequence bias in the cosmid and lambda libraries. Therefore, a new approach was devised for linking the sequenced regions which may be generally applicable. BAC libraries were constructed and terminal sequences of the clones were determined and used for both end mapping and PCR screening. The PCR approaches included a novel chromosome walking method termed "paired-PCR". 21 gaps were filled by BAC end sequence analyses and 6 gaps were filled by PCR including three large ones by paired-PCR. The complete map revealed that 0.9 Mb remained to be sequenced and 34 BAC clones were selected for walking over small gaps and preparing template libraries for larger ones. It is concluded that an optimal strategy for sequencing microorganism genomes involves construction of a high-resolution physical map by BAC end analyses, PCR screening and paired-PCR chromosome walking after about half the genome sequence has been accumulated.

Chromosomes, Artificial, Bacterial↗
PubMed1998

Completing the sequence of the Sulfolobus solfataricus P2 genome.

The Sulfolobus solfataricus P2 genome collaborators are poised to sequence the entire 3-Mbp genome of this crenarchaeote archaeon. About 80% of the genome has been sequenced to date, with the rest of the sequence being assembled fast. In this publication we introduce the genomic sequencing and automated analysis strategy and present intial data derived from the sequence analysis. After an overview of the general sequence features, metabolic pathway studies are explained, using sugar metabolism as an example. The paper closes with an overview of repetitive elements in S. solfataricus.

Base Sequence↗
PubMed1997

The complete genome sequence of the gram-positive bacterium Bacillus subtilis.

Bacillus subtilis is the best-characterized member of the Gram-positive bacteria. Its genome of 4,214,810 base pairs comprises 4,100 protein-coding genes. Of these protein-coding genes, 53% are represented once, while a quarter of the genome corresponds to several gene families that have been greatly expanded by gene duplication, the largest family containing 77 putative ATP-binding transport proteins. In addition, a large proportion of the genetic capacity is devoted to the utilization of a variety of carbon sources, including many plant-derived molecules. The identification of five signal peptidase genes, as well as several genes for components of the secretion apparatus, is important given the capacity of Bacillus strains to secrete large amounts of industrially important enzymes. Many of the genes are involved in the synthesis of secondary metabolites, including antibiotics, that are more typically associated with Streptomyces species. The genome contains at least ten prophages or remnants of prophages, indicating that bacteriophage infection has played an important evolutionary role in horizontal gene transfer, in particular in the propagation of bacterial pathogenesis.

Bacillus subtilis↗
PubMed1997

A Bacillus subtilis chromosome segment at the 100 degrees to 102 degrees position encoding 11 membrane proteins.

The 25.9 kbp region upstream of nprB at 100 degrees-102 degrees on the Bacillus subtilis chromosome was sequenced. This revealed a known gene, degA, which was previously mislocated on the genetic map. A total of 29 putative ORFs were identified including a cluster of three ORFs whose products show clear homology with sulphate adenylyl pathway enzymes and, in addition, 11 ORFs whose products have one or more membrane domains, as indicated by their hydropathy profiles.

Bacillus subtilis↗
PubMed1996

Hemodynamic and renal excretory effects of human brain natriuretic peptide infusion in patients with congestive heart failure. A double-blind, placebo-controlled, randomized crossover trial.

BACKGROUND: The pharmacological effects of infusion of human brain natriuretic peptide (hBNP) in patients with severe congestive heart failure have not been characterized previously. METHODS AND RESULTS: Twenty patients with severe congestive heart failure were randomized in a double-blind, placebo-controlled, crossover trial to receive incremental 90-minute infusions of hBNP (0.003, 0.01, 0.03, and 0.1 microgram/kg per minute) or placebo on 2 consecutive days. At the highest completed dose of the hBNP, mean pulmonary artery pressure decreased from 38.3 +/- 1.6 to 25.9 +/- 1.7 mm Hg; mean pulmonary capillary wedge pressure decreased from 25.1 +/- 1.1 to 13.2 +/- 1.3 mm Hg; mean right atrial pressure decreased from 10.9 +/- 1 to 4.8 +/- 1.0 mm Hg; mean arterial pressure decreased from 85.2 +/- 2.0 to 74.9 +/- 1.7 mm Hg; and cardiac index increased from 2.0 +/- 0.1 to 2.5 +/- 0.1 L/min per square meter (all P < .01 versus placebo). Urine volume and urine sodium excretion increased significantly during hBNP infusion when compared with placebo infusion (90 +/- 38 versus 67 +/- 27 mL/h and 2.6 +/- 2.4 versus 1.4 +/- 1.2 mEq/h, respectively, both P < .05 versus placebo), whereas creatinine clearance and urinary potassium excretion did not change. CONCLUSIONS: Infusion of incremental doses of hBNP is associated with favorable hemodynamic and natriuretic effects in patients with severe congestive heart failure.

Blood Pressure↗
PubMed1996

Changes in plasma endothelin-1 levels reflect clinical response to beta-blockade in chronic heart failure.

Plasma levels of endothelin-1 are elevated in patients with chronic heart failure; however, it is unknown whether changes in plasma endothelin-1 levels accurately reflect clinical response to therapy in these patients. To determine this, we measured plasma endothelin-1 in addition to functional, hemodynamic, and other neurohormonal parameters as part of a double-blind, placebo-controlled study of the beta-blocker vasodilator carvedilol in patients with moderate to severe chronic heart failure. Patients were assigned (2:1 randomization) to receive carvedilol (25 mg twice daily, n = 10) or placebo (n = 5) for 14 weeks, with evaluations made before and after therapy. Compared to patients receiving placebo, patients receiving carvedilol improved significantly as assessed by the parameters described. These changes were paralleled by significant falls in endothelin-1 with carvedilol (-2.1 + 3.8 pg/ml) in comparison to placebo (2.2 + 3.9 pg/ml; p < 0.05 for between-group differences). Changes in endothelin-1 after treatment in both groups correlated significantly with changes in symptom severity, New York Heart Association class, 6-minute walk distance (r = 0.64 to 0.80; p < 0.05), hemodynamic parameters (ejection fraction, right atrial pressure, pulmonary artery diastolic pressure, pulmonary wedge pressure, right atrial pressure, and stroke volume index; r = 0.54 to 0.86; p < 0.05), and neurohormonal parameters (serum aldosterone and plasma norepinephrine (r = 0.74 to 0.76; p < 0.05). By stepwise regression analysis, change in endothelin-1 was an independent, noninvasive predictor of functional and hemodynamic responses to therapy in these patients. These findings suggest that endothelin-1 accurately reflects functional, hemodynamic, and neurohormonal responses to beta-blocker therapy in patients with congestive heart failure. Measurement of endothelin-1 may therefore be a useful, noninvasive approach to the evaluation of clinical response to drug therapy in these patients.

Adrenergic beta-Antagonists↗
PubMed1995

Double-blind, placebo-controlled study of the long-term efficacy of carvedilol in patients with severe chronic heart failure.

BACKGROUND: Clinical trials have shown that beta-adrenergic blocking drugs are effective and well tolerated in patients with mild to moderate heart failure, but the utility and safety of these drugs in patients with advanced disease have not been evaluated. METHODS AND RESULTS: We enrolled 56 patients with severe chronic heart failure into a double-blind, placebo-controlled study of the vasodilating beta-blocker carvedilol. All patients had advanced heart failure, as evidenced by a mean left ventricular ejection fraction of 0.16 +/- 0.01 and a mean maximal oxygen consumption of 13.6 +/- 0.6 mL.kg-1.min-1 despite digitalis, diuretics, and an angiotensin-converting enzyme inhibitor (if tolerated). After a 3-week, open-label, up-titration period, 49 of the 56 patients were assigned (in a double-blind fashion using a 2:1 randomization) to receive either carvedilol (25 mg BID, n = 33) or matching placebo (n = 16) for 14 weeks, while background therapy remained constant. Hemodynamic and functional variables were measured at the start and end of the study. Compared with the placebo group, patients in the carvedilol group showed improved cardiac performance, as reflected by an increase in left ventricular ejection fraction (P = .005) and stroke volume index (P = .010) and a decrease in pulmonary wedge pressure, mean right atrial pressure, and systemic vascular resistance (P = .003, .002, and .017, respectively). In addition, compared with placebo, patients treated with carvedilol benefited clinically, as shown by an improvement in symptom scores (P = .002), functional class (P = .013), and submaximal exercise tolerance (P = .006). The combined risk of death, worsening heart failure, and life-threatening ventricular tachyarrhythmia was lower in the carvedilol group than in the placebo group (P = .028), but carvedilol-treated patients had more dizziness and advanced heart block. CONCLUSIONS: Carvedilol produces clinical and hemodynamic improvement in patients who have severe heart failure despite treatment with angiotensin-converting enzyme inhibitors.

Adrenergic beta-Antagonists↗
PubMed1995

Lymphocyte G proteins reflect response to treatment in congestive heart failure.

Congestive heart failure is associated with chronotropic and inotropic hyporesponsiveness to adrenergic stimulation. A decrease in Gs alpha or an increase in Gi alpha is associated with a decrease in adenylyl cyclase activity. The current study assessed G proteins in response to treatment with direct-acting vasodilators and correlated changes in lymphocyte beta-adrenergic receptor components with changes in hemodynamic variables. Twenty-three patients with severe chronic congestive heart failure (New York Heart Association functional classes III and IV) were studied. Patients were grouped as responders (n = 10) or nonresponders (n = 13) on the basis of clinical assessment of functional status from questionnaires. Therapy was associated with an increase in cardiac index, a decrease in mean arterial pressure, and a decrease in systemic vascular resistance in all patients. Left ventricular filling pressure significantly decreased in responders (26 +/- 2 mm to 13 +/- 3 mm, p < 0.05) but did not change significantly in nonresponders. Similarly, mean right atrial pressure significantly decreased in responders (11 +/- 2 mm Hg to 4 +/- 1 mm Hg, p < 0.05) but did not change in nonresponders. Plasma norepinephrine increased significantly only in nonresponders (679 +/- 100 pg/ml to 1233 +/- 201 pg/ml, p < 0.05). Whereas lymphocyte beta-adrenergic receptor density and Gs did not significantly change, Gi increased after treatment only in the nonresponder group (23 +/- 5 to 51 +/- 11 fmol/mg, p < 0.05). A poor response to direct-acting vasodilators can be distinguished by reactive increases in plasma norepinephrine and lymphocyte Gi in the absence of a decrease in either left- or right-sided filling pressures.

Aged↗
PubMed1993

Sustained hemodynamic response to flosequinan in patients with heart failure receiving angiotensin-converting enzyme inhibitors.

OBJECTIVES: We evaluated the short- and long-term effects of flosequinan in 47 patients with severe heart failure despite ongoing captopril treatment. BACKGROUND: There have been no previous evaluations of the long-term hemodynamic effects of any direct-acting vasodilator in patients with heart failure receiving an angiotensin-converting enzyme inhibitor. Flosequinan is an arterial and venous vasodilator with actions similar to those of the hydralazine-isosorbide dinitrate combination. METHODS: After baseline hemodynamic measurements using balloon-tipped pulmonary artery and radial arterial catheters, patients were randomized to receive 50, 100 or 150 mg of flosequinan daily. Hemodynamic variables were measured immediately before and after short-term flosequinan administration and after 8 weeks of therapy. RESULTS: With short-term flosequinan administration, mean arterial, right atrial and left ventricular filling pressures decreased by 6.4 +/- 1.1, 3.8 +/- 0.5 and 7.3 +/- 0.7 mm Hg, respectively (all p < 0.001). Cardiac index increased by 0.5 +/- 0.1 liters/min per m2, systemic vascular resistance decreased by 616 +/- 105 dynes.s.cm-5 and heart rate increased by 4 +/- 1 beats/min (all p < 0.001). After 8 weeks of long-term flosequinan administration, the vasodilator effect of a dose of flosequinan persisted. Compared with pretreatment baseline values, mean arterial, right atrial and left ventricular filling pressures at the peak effect of flosequinan were decreased by 3.5 +/- 1.3, 2.8 +/- 0.7 and 5.1 +/- 1.3 mm Hg, respectively (all p < 0.01). Systemic vascular resistance had decreased by 585 +/- 95 dynes.s.cm-5, cardiac index had increased by 0.5 +/- 0.1 liters/min per m2 and heart rate had increased by 10 +/- 2 beats/min (all p < 0.001). CONCLUSIONS: The arterial and venous vasodilator flosequinan exerts both short- and long-term sustained hemodynamic effects in patients with heart failure receiving angiotensin-converting enzyme inhibitors.

Adult↗
PubMed1991

Hemodynamic effects of renin inhibition by enalkiren in chronic congestive heart failure.

Previous efforts to block the renin-angiotensin system in patients with chronic congestive heart failure (CHF) have focused on 2 distal sites in the system, the angiotensin-converting enzyme and the angiotensin II receptor. Recent work, however, has led to the development of agents that directly inhibit renin, the proximal step in the cascade. In this study, we investigated the hemodynamic effects of renin inhibition in 9 patients with chronic CHF by using enalkiren, a primate-selective, dipeptide renin inhibitor, which has been previously shown to suppress plasma renin activity and to lower blood pressure in hypertensive patients. The acute intravenous administration of enalkiren (1.0 mg/kg) produced increases in cardiac index (2.0 +/- 0.3 to 2.3 +/- 0.1 liter/min/m2) and stroke volume index (26 +/- 3 to 34 +/- 4 ml/m2) and decreases in left ventricular filling pressure (31 +/- 3 to 25 +/- 3 mm Hg), mean right atrial pressure (15 +/- 1 to 13 +/- 2 mm Hg), heart rate (78 +/- 5 to 72 +/- 6 beats/min) and systemic vascular resistance (2,199 +/- 594 to 1,339 +/- 230 dynes.s.cm-5) (all p less than 0.01 to 0.05). These observations indicate that renin inhibition produces hemodynamic benefits in patients with chronic CHF and could potentially provide a novel approach to interfering with the renin-angiotensin system in patients with this disorder.

Adult↗
PubMed1990

Comparative hemodynamic effects of procainamide, tocainide, and encainide in severe chronic heart failure.

Many of the newer antiarrhythmic agents are said to cause minimal myocardial depression, but their hemodynamic effects have not been invasively evaluated and compared in patients with severe chronic heart failure. In a randomized, crossover study, the hemodynamic responses to single oral doses of procainamide (750 mg), tocainide (600 mg), and encainide (50 mg) given to 21 patients with severe chronic heart failure were compared. Cardiac performance decreased with all three drugs, but the magnitude of deterioration differed among the three agents. Stroke volume index decreased with procainamide (-5 +/- 1 ml/m2, p less than 0.001), tocainide (-7 +/- 1 ml/m2, p less than 0.001), and encainide (-8 +/- 1 ml/m2, p less than 0.001), but the decline was significantly greater with encainide than with procainamide (p less than 0.05). Similarly, left ventricular filling pressure increased with tocainide and encainide (+4 +/- 1 and +5 +/- 2 mm Hg, respectively; both p less than 0.05), but not with procainamide; the increase was significantly greater with tocainide and encainide than with procainamide (p less than 0.001). These deleterious hemodynamic effects were accompanied by worsening symptoms of heart failure in six patients with encainide and seven patients with tocainide but in only two patients with procainamide. Serum levels for all drugs were in the therapeutic range. In conclusion, although the three type I antiarrhythmic agents tested may all adversely affect left ventricular function in patients with heart failure, encainide and tocainide are more likely than procainamide to cause hemodynamic and clinical deterioration.

Aged↗
PubMed1989

Adverse hemodynamic and clinical effects of encainide in severe chronic heart failure.

STUDY OBJECTIVE: To evaluate the hemodynamic effects of the antiarrhythmic drug, encainide, in patients with severe chronic heart failure. DESIGN: Unblinded, before-after study. SETTING: Referral center for patients with heart failure. PATIENTS: Thirty patients with severe chronic heart failure and a left ventricular ejection fraction less than 40%. INTERVENTIONS: Invasive hemodynamic measurements were done (using a balloon-tipped thermodilution catheter) before and for 3 hours after a single oral dose of 50 mg of encainide. MEASUREMENTS AND MAIN RESULTS: Ninety to one hundred and twenty minutes after its administration, encainide produced a significant deterioration in cardiac performance, as reflected by a fall in cardiac index from 2.3 to 1.8 L/min.m2 body surface (mean change 0.5 +/- 0.1; P less than 0.001), a fall in stroke work index from 26 to 18 g.m/m2 (mean change 8 +/- 2; P less than 0.001), and an increase in left ventricular filling pressure from 19 to 22 mm Hg (mean change 3 +/- 2; P less than 0.05). These deleterious hemodynamic effects were accompanied by worsening symptoms of heart failure in 8 of the 30 patients. Serum levels of encainide and its metabolites, O-desmethylencainide and 3-methoxy-O-desmethylencainide, were within the therapeutic range in most patients. CONCLUSIONS: Encainide can cause adverse hemodynamic and clinical effects in patients with severe chronic heart failure.

Adult↗
PubMed1988

Cumulative hemodynamic response to short-term treatment with flosequinan (BTS 49465), a new direct-acting vasodilator drug, in severe chronic congestive heart failure.

Pharmacologic tolerance develops rapidly to the hemodynamic effects of many vasodilator drugs used in the treatment of congestive heart failure. We evaluated the responses to 3 days of therapy with a new long-acting vasodilator drug, flosequinan (BTS 49465), in 16 patients with severe chronic heart failure. On each of the 3 days, flosequinan (100 or 150 mg orally) produced marked increases in cardiac index and decreases in left ventricular filling pressure, mean right atrial pressure, and systemic vascular resistance (all p less than 0.01) without significant changes in heart rate. Whereas the effects of flosequinan on right and left ventricular filling pressures on the first and third days were similar, cardiac index was higher and systemic vascular resistance was lower after the third dose than after the first dose of the drug, indicating the occurrence of a cumulative vasodilator effect on arterial resistance vessels. Since all hemodynamic changes persisted for longer than 24 h after each dose of the drug, the daily administration of flosequinan also produced a progressive improvement in the hemodynamic state recorded before each dose of the drug. These data indicate that pharmacologic tolerance does not develop to the effects of flosequinan during short-term therapy with the drug in patients with severe chronic heart failure. Instead, further hemodynamic improvement may occur because of a cumulative vasodilator effect that results from the drug's prolonged duration of action.

Adult↗