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Biomedical subjects

M Das

Publications and source records attributed to M Das.

At least 325 records · Page 18Linked to original sources
PubMed1977

Specific radiolabeling of a cell surface receptor for epidermal growth factor.

A photoreactive derivative of epidermal growth factor (EGF) has been used to identify and specifically label a membrane receptor for EGF on mouse 3T3 cells. Photoactivable EGF, labeled with 125I, was incubated with 3T3 cells and then photolyzed in situ to generate a nitrene capable of reacting with a wide variety of chemical bonds. Analysis of the system by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed, besides the band of EGF, only one other major radioactive band, at a position indicating an apparent molecular weight of 190,000. This band was absent when a nonresponsive and nonbinding variant of 3T3 was used. A direct proportionality between binding activity and crosslinked complex formation was demonstrated using a variety of binding conditions. "Down regulated" cells, in which EGF binding activity was greatly reduced by prolonged incubation with an appropriate concentration of EGF, also had a decrease in covalent complex formation proportional to the decrease in EGF binding activity.

Affinity Labels↗
PubMed1977

Metabolic correlates of immune dysfunction in malnourished children.

Mononuclear cells of malnourished children contain diminished activity of phosphoglycerate kinase and pyruvate kinase (PK). The PK activity of these cells correlates well with the percentage of circulating thymus-derived lymphocytes (T-cells). Phytohemagglutinin causes an immediate increase in PK activity of mononuclear cells of malnourished patients. The correlation of PK activity with T-cells and the response of PK activity to phytohemagglutinin are in distinct contrast to observed perturbations of neonatal mononuclear cell metabolism. The relationship of the metabolic alterations to the pathophysiology of the immune system in malnutrition has not yet been defined.

Adolescent↗
PubMed1977

Glycolytic metabolism of neonatal mononuclear cells.

The mononuclear cells of newborn infants compared to those of normal adults contain diminished activity of pyruvate kinase (PK) (14.9 +/- 1.2 vs. 22.3 +/- 1.3 mumol/10(10) cells/min) and phosphoglycerate kinase (PGK) (195 +/- 10 vs. 415 +/- 19). These deficiencies are accentuated in the cells of premature infants (4.9 +/- 0,5 and 71 +/- 15, respectively) and are accompanied by reduced activity of adenylate kinase (AK) (14.8 +/- 1.9 vs. 33.6 +/- 2.6). The activities of AK and PGK in adult and neonatal mononuclear cells are stimulated by phytohemagglutinin (PHA). Although the PK activity of adult cells is stimulated by PHA, the PK activity of neonatal cells is not. Mononuclear cell glycolysis is stimulated by PHA in both adults and neonates. The mean lactate production of neonatal cells is slightly lower than it is in adult cells (93 vs. 110 mumol/10(10) cells/hr, unstimulated, and 151 vs. 181, stimulated), but the differences are not statistically significant. The ATP content of neonatal cells (3.8 +/- 0.4 mumol/ 10(10) cells) is reduced compared to adult values (6.0 +/- 0.3). Lactate production is directly correlated with PK activity in adult and neonatal mononuclear cells. Neonatal mononuclear cell PK activity increases to adult levels during the first year of life.

Adenosine Triphosphate↗
PubMed1976

Pulmonary angiotensin-converting enzyme antienzyme antibody.

A method has been developed for quantitating anticatalytic activity in antibody preparations made in goats against pure solubilized angiotensin-converting enzyme from rabbit pulmonary membranes. Anticatalytic activity was purified about 90-fold from a single batch of serum by a procedure including diethylaminoethylcellulose chromatography and elution from Sepharose columns containing covalently bound pure enzyme. Antiholoenzyme antibody was fractionated with respect to charge and binding affinity; however, these different populations each inhibited enzymatic hydrolysis of hippurylhistidylleucine, angiotensin I, and bradykinin. The inhibition dose-response curves were similar for hydrolysis of hippurylhistidylleucine and angiotensin I despite the difference in molecular weight of these substrates. Evidence is presented suggesting that a single molecule of antibody can bind two molecules of enzyme and that at least 18% of the total antiholoenzyme antibody population is directed against determinants which influence catalytic activity. A competitive immunoassay was developed with radioiodinated pulmonary enzyme as displaceable antigen. The anticatalytic and radioimmune assays were used to examine immunological properties of converting enzymes in various rabbit organs and fluids. Kidney, brain, and serum were found to contain converting enzymes which were immunologically identified with that in rabbit lung. Converting enzyme in seminal plasma was similar to the lung enzyme in the anticatalytic assay, but showed lower immunoreactivity in the radioimmune assay.

Animals↗
PubMed1976

Angiotensin-converting enzyme: vascular endothelial localization.

Fluorescein-labeled antibody to rabbit pulmonary angiotensin-converting enzyme localized in the vascular endothelium of rabbit lung, liver, adrenal cortex, pancreas, kidney, and spleen. Epithelial cells of the renal proximal tubules were the only parenchymal cells among the organs studied that demonstrated immunoreactivity.

Adrenal Cortex↗
PubMed1976

Morphological, histochemical, autoradiographic and topographical evidences of the origin of the Langerhans' cell from the melanocyte in the skin of the guinea pig.

The microscopic anatomy of the nucleus, Golgi substance, mitochondria, etc. of type 1, 2, 3 and 4 albino melanocytes, type 01 and 011 albino intermediate cells of Billingham and Medawar and type I, II, III and IV albino Langerhans' cells of the albino guinea pig, is presented in detail. The study has demonstrated that the albino melanocytes degenerate through sequential stages of intermediate cells of Billingham and Medawar, type I, II and III Langerhans' cells to ultimately from type IV Langerhans' cells. It has been shown that all the dendritic cells of the epidermis belonged to one class of cells. Autoradiographic techniques have shown that type 3 and type 4 melanocytes, respectively, bearing 6 and 5 round-tipped dendritic processes, divide by mitosis to form two daughter cells. One of these two daughter forms the intermediate cell of Billingham and Medawar. This cell, while transforming sequentially into type I, II, III and IV Langerhans' cells, moves up through the Malpighian and granular layers of cells, to the stratum corneum. This type IV Langerhans' cell is ultimately extruded out of the stratum corneum by exfoliation. The other daughter melanocyte remains at its place in the sub-basal zone to function as a mature melanocyte. The time for the passage of the daughter melanocyte to travel from the sub-basal zone to the stratum corneum layer was found to be 15 days.

Animals↗
PubMed1975

Pulmonary angiotensin-converting enzyme. Structural and catalytic properties.

Angiotensin-converting enzyme has been solubilized from a particulate fraction of rabbit lung and purified to apparent homogeneity in 11% yield by a procedure including fractionation with DEAE-cellulose and calcium phosphate gel, elution from Sephadex G-200, and lectin affinity chromatography. The molecular weight estimated by equilibrium sedimentation was approximately 129,000, either in the absence or presence of 6 M guanidine hydrochloride. A slightly higher value of 140,000 determined for the reduced, denatured protein by gel electrophoresis in the presence of sodium dodecyl sulfate and a much higher figure derived from gel filtration are probably due to the glycoprotein nature of the enzyme. Its oligosaccharide content accounted for 26% of the weight calculated from its amino acid and carbohydrate composition. The estimated content of sugar residues per mole was: galactose, 57; N-acetylglucosamine, 53; mannose, 43; N-acetylneuraminic acid, 19; and fucose, 4. Threonine and alanine were identified, respectively, as NH2-terminal and COOH-terminal residues by the dansylation procedure and by digestion with carboxypeptidase A. The enzyme was found to contain approximately 1 g atom of zinc per mol. Km values for hydrolysis of hippurylhistidylleucine and angiotensin I were 2.3 and 0.07 mM, and the corresponding turnover numbers were 15,430 and 792 mol/min/mol at 37 degrees. Bradykinin was also a substrate, and release of its COOH-terminal dipeptide, Phe-Arg, was catalyzed at a comparable rate to that of His-Leu from the COOH terminus of angiotensin I. Enzyme activity required the presence of chloride ions and was inhibited by EDTA and by low concentrations of Bothrops bradykinin-potentiating peptides. In addition, hydrolysis of hippurylhistidylleucine was inhibited competitively by other defined peptides, including di- and tripeptides, which were not substrates.

Amino Acids↗
PubMed1975

Studies on a wide-spectrum intestinal dipeptide uptake system in the monkey and in the human.

1. The intestinal transport of glycine and leucine residues of glycyl-L-leucine was studied in the monkey and in the human in vitro. Uptake of both [14C]glycyl-L-leuine and glycyl-L-[14C]leucine show similar Kt values, but there is a marked difference in the Vmax. values. Preliminary studies suggest that this anomalous difference in the Vmax. values may be due to the greater efflux rate of glycine from the tissue. 2. Arrhenius plots of both [14C]glycyl-L-leucine uptake and glycyl-L-[14C]leucine uptake in the monkey intestine show a discontinuity at about 20 degrees C. The activation energies above and below the discontinuity are similar for both [14C]glycyl-L-leucine uptake and glycyl-L-[14C]leucine uptake. These similarities in uptake characteristics suggest that the dipeptide glycyl-L-leucine is transported as one unit. 3. In the monkey intestine, glycyl-L-leucine uptake is inhibited by a wide variety of dipeptides, including those containing acidic and basic amino acids. The inhibition was shown to be competitive by using four representative dipeptides namely: L-alanyl-L-alanine, L-alanyl-L-leucine, L-glutamyl-L-glutamic acid and L-lysyl-L-lysine. The results strongly suggest that in the monkey intestine there may be a dipeptide-uptake system with an extremely broad specificity. These results were also confirmed in the human in a limited way.

Alanine↗
PubMed1973

Glycyl-L-leucine hydrolase, a versatile 'master' dipeptidase from monkey small intestine.

1. A highly active and electrophoretically homogeneous dipeptidase was purified from the soluble extracts of monkey small-intestinal mucosa. 2. By gel-filtration studies the molecular weight of the enzyme was found to be 107000. It is composed of two identical, subunits of molecular weight 54000. 3. A paper-chromatographic method of dipeptidase assay was developed to overcome some of the difficulties encountered in the generally used spectrophotometric procedure. By using this method, the K(m) and k(0) values of a few substrates were determined. 4. The substrate specificity of the enzyme was investigated in great detail with substrates of a wide range of possible structural types. The enzyme hydrolyses a very large proportion of the range of dipeptides tested. This enzyme, which exhibits such a wide range of action, has been termed the ;master' dipeptidase of the intestine. Glycylglycine, glycyl-l-proline, glycyl-l-histidine, l-prolylglycine and some of the arginine- and aspartic acid-containing dipeptides were not substrates and are possibly hydrolysed by other peptidases. These results therefore suggest that in the intestine the number of dipeptidases is rather limited. 5. In the light of these findings, the implications on the role of dipeptidases in intestinal peptide transport are discussed.

Animals↗