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Biomedical subjects

J Glass

Publications and source records attributed to J Glass.

At least 109 records · Page 6Linked to original sources
PubMed1985

Iron uptake in reticulocytes. Inhibition mediated by the ionophores monensin and nigerisin.

The lipophilic carboxylic ionophores monensin and nigerisin reversibly blocked iron uptake by erythroid cells. At low concentrations of ionophores (0.25-0.5 microM), the disruption of the compartment in which iron is released affected minimally the release of iron from transferrin but effectively inhibited iron uptake. Iron released from transferrin was extruded from the cell synchronously with but not bound to transferrin. The compartment disrupted by the ionophores, and in which iron is released from transferrin, is apparently contiguous to the extracellular medium. Contiguity was assessed by determining the effect of extracellular Na+ and K+ on the activity of the ionophores. The above data fit a model of iron uptake in which iron is released from transferrin in an acidic compartment in immediate contiguity with the cell plasma membrane. Iron is then bound by its membrane acceptor and is translocated to the cytosolic side of the plasma membrane. At submicromolar concentrations, the ionophores monensin and nigerisin produce a small increase in the pH of the acidic compartment. The pH change, which is not sufficient to block the release of iron from transferrin, is enough to block the binding of released iron to its acceptor in the plasma membrane, thus producing inhibition of iron uptake.

Animals↗
PubMed1985

Household structure and labor force participation of black, hispanic, and white mothers.

This paper investigates whether the inclusion of nonnuclear adults in a household facilitates the labor force participation of single and married mothers. Results based on a sample of extended and nuclear households show that the extension mechanism facilitates the labor market entry of married mothers, but not of single mothers. Interactions between extended structure, ethnicity, and poverty, however, suggest a complex relationship. For extended family households, the gender and employment characteristics of nonnuclear adults affected the labor force participation of single mothers, but the number of nonnuclear members was inversely associated with the market activity of married mothers. Policy implications are discussed in the final section.

Black or African American↗
PubMed1984

Beta globin messenger RNA content of bone marrow erythroblasts in heterozygous beta-thalassemia.

RNA from bone marrow erythroblasts and peripheral blood reticulocytes of patients with heterozygous beta-thalassemia was analyzed for relative content of alpha and beta globin messenger RNA by molecular hybrization. Erythroblasts from nonthalassemic patients exhibited approximately the same alpha and beta globin mRNA content (beta/alpha mRNA ratio = 0.8-1.0) as circulating reticulocytes (beta/alpha mRNA ratio = 0.74-1.2). The mRNA ratios corresponded well to levels of globin synthesis observed in bone marrow and peripheral blood. Erythroblasts from four patients with heterozygous beta-thalassemia also exhibited approximately the same beta/alpha mRNA ratios in bone marrow erythroblasts (0.34-0.59) as in reticulocytes (0.34-0.4): beta globin mRNA was clearly deficient in bone marrow erythroblasts. Globin biosynthesis by erythroblasts of beta-thalassemia heterozygotes was balanced despite the mRNA deficiency (beta/alpha = 0.9-1.0), suggesting that post-translational phenoma (eg, proteolysis of free globin chains), rather than instability of beta mRNA, accounts for the balanced globin chain synthesis frequently observed in bone marrow erythroblasts of patients with beta-thalassemia trait.

Adult↗
PubMed1983

The transferrin cycle and iron uptake in rabbit reticulocytes. Pulse studies using 59Fe, 125I-labeled transferrin.

Rabbit reticulocytes were pulsed for 10 s with diferric 59Fe, 125I-labeled transferrin followed without further manipulation by a chase with unlabeled diferric transferrin. The 125I-transferrin and 59Fe were measured in different cell compartments as a function of time thereafter. Immediately after binding, transferrin entered a phase that lasted 60 s, characterized by a slow dissociation of transferrin into the extracellular medium. During this period, most of the iron originally present in transferrin is donated to the cell. The half-time of 59Fe release from transferrin was 43 s. After the initial 60 s, transferrin, now devoid of iron, is released into the medium. The whole transferrin cycle lasted about 4 min. The iron released from transferrin could be transiently found in the cell plasma membrane, the cytosol, and the mitochondria. All these compartments behaved like intermediates in the iron uptake process as their 59Fe content rose, reached a plateau, and gradually fell. Finally, the iron was incorporated into heme with a half-time of incorporation of 173 s. We conclude that the release of iron from transferrin is one of the fastest events occurring after the initial binding of transferrin. The limiting step in the entire process of iron delivery is the dissociation of apotransferrin from its receptor, a step which will enable the latter to undergo another cycle of transferrin binding.

Animals↗
PubMed1982

Reconstitution of the transferrin receptor in lipid vesicles. Effect of cholesterol on the binding of transferrin.

Purified rabbit reticulocyte transferrin receptors were incorporated into phosphatidylcholine vesicles containing varying amounts of cholesterol. The binding of transferrin to the receptor in the reconstituted vesicles had three distinct characteristics: (1) The binding of transferrin exhibited the two components characteristic of transferrin binding to erythroid cells, a saturable, specific component and a nonsaturable, nonspecific component. (2) Transferrin binding exhibited positive cooperativity at low cholesterol/phospholipid (C/P) molar ratios. However, the cooperativity diminished and then disappeared as the C/P molar ratios were increased to the levels found in circulating red blood cells. (3) The amount of specific transferrin binding to the reconstituted vesicles also decreased as the C/P molar ratio was increased. These results indicate that in the reconstituted system the lipid environment plays a significant role in the expression of transferrin receptors.

Animals↗
PubMed1981

Accumulation of the prolipoprotein of the Escherichia coli outer membrane caused by benzyloxycarbonylalanine chloromethyl ketone.

Benzyloxycarbonylalanine chloromethyl ketone (Z-Ala-CH2Cl) was found to inhibit the processing of the prolipoprotein, a secretory precursor of the lipoprotein of the Escherichia coli outer membrane. The accumulation of the prolipoprotein in the presence of Z-Ala-CH2Cl was observed both in vivo and in vitro. Z-Ala-CH2Cl did not inhibit the processing of precursors of the other major outer membrane proteins. A preliminary experiment to identify the processing enzyme(s) of the prolipoprotein was carried out with use of Z-[3H]Ala-CH2Cl and revealed that two cytoplasmic membrane proteins with Mr = 78,000 and 46,000 were predominantly labeled.

Amino Acid Chloromethyl Ketones↗
PubMed1981

the stability in various detergents of transferrin-transferrin receptor complexes from reticulocyte plasma membranes.

Transferrin-membrane protein complexes were solubilized either with 0.4% sodium dodecyl sulfate (SDS), 1% Triton X-100 or 0.5% sulfobetaine 3-14 from the plasma membranes of rabbit reticulocytes previously labeled with 125I and then incubated with 131-labeled transferrin. When the solubilized membranes were analyzed by gel filtration fractionation, marked variation in the preservation of transferrin-transferrin receptor interaction was noted between the three detergents. After SDS solubilization, more than 80% of the 131I-labeled transferrin remained associated with membrane proteins with apparent molecular weight of the transferrin-receptor complexes of 1400 000 and 240 000. In contrast, after Triton X-100 solubilization only 40% of the transferrin was still complexed to membrane proteins with an apparent molecular weight of the complex of 450 000. Dissociation of transferrin from its receptor was most marked following sulfobetaine solubilization, with less than 30% of the transferrin still complexed. Following gel filtration 131I-labeled transferrin-125I-labeled membrane protein complexes were immunoprecipitated with goat specific anti-rabbit transferrin antibodies. The immunoprecipitates were analyzed under stringent dissociating conditions by two SDS-polyacrylamide gel electrophoretic techniques. In a linear 5-25% polyacrylamide gradient the 125I-labeled receptor obtained after membrane solubilization with all three detergents had an apparent molecular weight of 80 000. In contrast, in a different system using 10% polyacrylamide gel two 125I-labeled receptor components were detected wih apparent molecular weights of 90 000 and 80 000. These results demonstrate that estimates of the molecular weight of the transferrin receptor depended on the conditions of electrophoresis and suggest that the transferrin receptor is partially modified, perhaps by glycosylation.

Animals↗
PubMed1981

Nebulised cromoglycate, theophylline, and placebo in preschool asthmatic children.

Sixteen children aged under 5 years with chronic asthma completed a double-blind crossover trial of treatment with oral choline theophyllinate (6.7 mg/kg four times daily) and nebulised sodium cromoglycate (20 mg four times daily). The trial comprised three 8-week treatment periods during which active sodium cromoglycate, active choline theophyllinate, and placebo were given in random order. Symptom scores for sleep disturbance, cough, wheeze, and daily activities were similar during the three treatment periods if results were analysed using Friedman's non-parametric analysis of variance. However the Mantel-Haenszel test showed that sodium cromoglycate was superior to placebo (P less than 0.05) in maintaining normal daily activities. Either regimen is safe and well tolerated by young children.

Activities of Daily Living↗
PubMed1981

Radiotherapy as a cause of complete atrioventricular block in Hodgkin's disease. An electrophysiological-pathological correlation.

A 20-year-old man contracted Hodgkin's disease and was treated with mantle radiotherapy. Heart block developed 11 years later. Electrocardiograms revealed predominant atrioventricular (AV) block and occasional AV conduction. Intracardiac electrograms demonstrated that the site of AV block was above the level of the His bundle. A permanent transvenous pacemaker was implanted. Seven months later the patient died of complications from cryptococcal meningitis. Pathological study of the heart revealed marked arteriosclerosis with fibrosis of the epicardium, myocardium, and endocardium. Examination of the conduction system revealed extensive arteriolosclerosis of the sinoatrial node and its approaches. In addition, there was marked fibrosis of the approaches to the AV node, the AV bundle, and both bundle branches. There was no evidence of Hodgkin's disease. This case documents the rare occurrence of AV block due to tissue destruction by radiotherapy. There was a good correlation between block proximal to the His bundle recording site and fibrosis of the approaches to the AV node.

Adult↗
PubMed1980

Different base per unit length ratios exist in single-stranded RNA and single-stranded DNA.

A significant difference was found to exist in the number of bases per unit length of single-stranded RNA as compared to single-stranded DNA when single-stranded RNA or DNA molecules of known nucleotide sequence were measured by electron microscopy using a cytochrome spreading technique. Using this technique, single-stranded RNA was found to have 17.5% more bases per unit of length than single-stranded DNA. These ratios were verified using four different denaturing conditions for the RNA: 80% formamide, 80% formamide plus glyoxal, 80% formamide/4M urea and 80% formamide/4M urea plus glyoxal. Molecules ranging in size from 1541 to 5386 nucleotides were examined and the number of bases per unit length was found to vary inversely with micrometer was consistent when RNA and DNA molecules of the same length were compared.

DNA, Single-Stranded↗