A common step for signal transduction in G protein-coupled receptors.
Explore the source record for details and available documents.
Allosteric Regulation↗
Biomedical subjects
L Oliveira
Publications and source records attributed to L Oliveira.
[Treatment of colonic atresia. Report of 3 cases].
Atresia of the colon (AC) is an uncommon cause of neonatal intestinal obstruction requiring prompt surgery. However, its optimal operative management is matter of discussion. We report the surgical therapy and evolution of three cases successfully treated at our department. A type I case was submitted to a coloplasty plus resection of the diaphragm; two cases of type III underwent a two-staged procedure, i.e., colostomy with subsequent anastomosis without resection. After analysing the different operative procedures we suggest that a colostomy with later establishment of intestinal continuity may be an advantageous procedure even in the healthy patients with proximal lesions. A coloplasty is a safe alternative to type I atresias.
Colon↗
Horse urinary kallikrein, I. Complete purification and characterization.
The isolation procedure for horse urinary kallikrein was considerably improved by the introduction of two new purification steps: a) removal of mucoproteins and concentration of the urine by ultrafiltration and b) affinity chromatography on benzamidine-Sepharose conjugate. The homogeneity of the enzyme preparations, regarding their protein moiety, was demonstrated by: 1) a single symmetric peak on DEAE-Sephadex chromatography, with constant values for A280/A260 ratios, esterolytic and amidolytic specific activities; 2) a single band, although dispersed, on gel-electrophoresis at pH 8.3, also in the presence of sodium dodecyl sulfate, and 3) a unique sequence for the six amino-terminal residues. The isolated enzyme was shown to be a single chain glycoprotein (alpha-kallikrein), similar to human urinary and porcine-pancreatic kallikreins regarding the protein moiety molecular mass, amino-acid composition, and partial amino-terminal sequence; differences were found in their total sugar content and even more conspicuously in their carbohydrate composition. In contrast to porcine pancreatic beta-kallikrein, horse urinary kallikrein was not substrate-activated and unlike other alpha-kallikreins, did not present the biphasic time-course in benzoyl-L-arginine ethyl ester hydrolysis. The specificity constants (kcat/Km) for ester and 4-nitroanilide substrates were lower for horse urinary than for pancreatic beta-kallikrein and as observed with the latter enzyme, were affected by NaCl.
Amino Acids↗
Horse urinary kallikrein, II. Effect of subsite interactions on its catalytic activity.
The effect of secondary-subsite interactions on the catalytic efficiency of horse urinary kallikrein was studied using as substrates oligopeptides and peptidyl-4-nitroanilides with L-Arg at P1. The known secondary specificity of tissue kallikreins for hydrophobic residues at P2 was also demonstrated for horse urinary kallikrein and a higher preference of this enzyme for L-Phe over L-Leu at P2 was evident. Interaction of subsites S3 with D-Pro and D-Phe enhanced the catalytic efficiency but tripeptidyl-4-nitroanilides with acetyl-D-Pro, L-Pro and acetyl-L-Pro at P3 were no better substrates than acetyl-dipeptidyl-4-nitroanilides. The importance of the leaving group for the catalysis was proved by higher kcat/Km values for the peptides in relation to peptidyl-4-nitroanilides containing a common acyl-chain. The low kcat value for the peptide with L-Pro at P'2 stresses the importance of a hydrogen bond between P'2 amide and the carbonyl group at S'2. One L-arginine residue at the leaving group, specially at the P'2 position, decreases the value of the apparent Km. This effect resulting of side-chain interactions with S'2, is impaired by a second L-Arg at P'1.
Animals↗
Interaction of narcotic antagonist naltrexone with nicotinic acetylcholine receptor.
The interactions of naltrexone with the nicotinic acetylcholine receptor were studied electrophysiologically using the frog sciatic nerve-sartorius muscle and biochemically using membranes from the electric organ of Torpedo ocellata. At nanomolar concentrations naltrexone increased the peak amplitude of endplate currents with little change in the decay time constant. At micromolar concentrations there was a concentration-dependent depression of endplate current and miniature endplate current amplitudes and decay time constants. Decay time constant depression was enhanced with hyperpolarization. Only marginal curvature was induced in peak endplate current amplitude versus membrane voltage plots by naltrexone. Naltrexone had no effect on single channel conductance but decreased open channel lifetime, according to fluctuation analysis. Naltrexone alone (less than or equal to 3 microM) did not impair binding of [125I]alpha-bungarotoxin to the receptor in a fast pre-equilibration assay, but increased the ability of acetylcholine to displace [125I]alpha-bungarotoxin. The drug displaced the agonist-stimulated binding of [3H]perhydrohistrionicotoxin to the channel site. Biphasic functional changes in neuromuscular transmission can be attributed to an allosteric mechanism with increased agonist binding to the nicotinic receptor at nanomolar concentrations and caused a non-competitive blockade of the ionic channel at micromolar concentrations.
Amphibian Venoms↗
Substrate activation of porcine pancreatic kallikrein by N alpha derivatives of arginine 4-nitroanilides.
Hydrolysis of several N alpha-substituted L-arginine 4-nitroanilides with porcine pancreatic kallikrein was studied under different conditions of pH, temperature, and salt concentration. At high substrate concentrations a deviation from Michaelis-Menten kinetics was observed with a significant increase in the hydrolysis rates of almost all substrates. Kinetic data were analyzed on the assumption that porcine pancreatic kallikrein presents an additional binding site with lower affinity for the substrate. Binding to this auxiliary site gives rise to a modulated enzyme species which can hydrolyze an additional molecule of the substrate through a second catalytic pathway. The values of both Michaelis-Menten and catalytic rate constants were higher for the modulated species than for the free enzyme, suggesting a mechanism of enzyme activation by substrate. Kinetic data indicated similar substrate requirements for binding at the primary and auxiliary sites of the enzyme. Tris(hydroxymethyl)aminomethane hydrochloride and NaCl were shown to alter the kinetic parameters of the hydrolysis of N alpha-acetyl-L-Phe-L-Arg 4-nitroanilide by porcine pancreatic kallikrein but not the enzyme activation pattern (ratio of the catalytic constants for the activated and the free enzyme forms). Similar observations were made when the hydrolysis of D-Val-L-Leu-L-Arg 4-nitroanilide was studied under different pH and temperature conditions.
Anilides↗
Computation of ventilation-perfusion ratio with Kr-81m in pulmonary embolism.
Diagnostic difficulties occur in pulmonary embolism (PE) during visual analysis of ventilation-perfusion images in matched defects or in chronic obstructive lung disease (COPD). In 44 patients with angiographically confirmed PE and in 40 patients with COPD, the regional ventilation-perfusion ratios (V/Q) were therefore computed using krypton-81m for each perfusion defect, and were displayed in a functional image. In patients with PE and mismatched defects, a high V/Q (1.96) was observed. A V/Q greater than 1.25 was also found in nine of 11 patients having PE and indeterminate studies (studies with perfusion abnormalities matched by radiographic abnormalities). COPD was characterized by matched defects and low V/Q. The percentage of patients correctly classified as having PE or COPD increased from 56% when considering the match or mismatched character to 88% when based on a V/Q of 1.25 in the region of the perfusion defect. This quantitative analysis, therefore, seems useful in classifying patients with scintigraphic suspicion of PE.
Adult↗
[Predictive factors of hospital and 6-month morbidity and mortality in hospitalized elderly patients].
This article presents the results of a prospective multivariable study of elderly patients aged over 70 years, hospitalized in an Internal Medicine Department of a Central Lisbon Hospital. The study aimed to identify, at the beginning of hospital admission (HA), predictive factors of hospital mortality (HM) and mortality at 6 months, of duration of HA, of admission to a nursing home at the time of discharge and during a period of 6 months thereafter and of hospital readmission during the 6 months following discharge. The study included 158 patients with a mean hospital stay of 15 days and a hospital mortality of 12%. The main pathologies responsible for hospital admission were cerebrovascular accident (22%), heart failure (20%) and pneumonia (16%). Mortality at 6 months was 29% and hospital readmission in the 6 months thereafter was 24%. When the patient was cared for by the spouse there was a statistically significant correlation with a shorter duration of admission (p = 0.006). Mean hospital stay was not significantly associated with any other variable. A subjective medical evaluation (SME) at the start of HA (p = 0.001), a low Barthel score prior to and at the time of HA, low serum albumin (p = 0.001) and a high leucocyte count (p = 0.005) were correlated with a higher HM. Nursing home admission was only positively correlated with cerebrovascular pathology. Mortality at 6 months was significantly correlated with the SME (p = 0.001), a low Barthel score prior to admission (p < 0.008) and at the time of HA (p < 0.001), nursing home residency (p < 0.005) and a low mental test score (p < 0.01). Hospital readmission at 6 months was influenced by the SME (p < 0.04) and by the reduction in the Barthel score caused by the illness and HA (p = 0.004). These correlations enabled the development of mathematical models that predict HM and mortality at 6 months and admission to a nursing home at the time of discharge and during a period of 6 months thereafter. They could be important in identifying elderly patients' needs early in the hospital admission and in the improvement of the strategy necessary for a successful and dignified hospital discharge.
Aged↗