摘要:

AbstractHuman breast cancer cell lines have been shown to possess high affinity receptors for 1,25‐dihydroxyvitamin D3 (1,25(OH)2D3) on the activity of glucose‐6‐phosphate dehydrogenase (G6PD) in cells of a human breast cancer cell line MCF‐7. G6PD, an enzyme which controls the hexose monophosphate shunt, is elevated and sensitive to 17β‐estradiol in breast tumors. G6PD activity was stimulated by 1,25(OH)2D3 in a dose‐dependent manner at very low concentrations of steroid (10−10–10−12M). 1,25(OH)2D3 increased maximum velocity without modifying the affinity constant of the enzyme for g

ISSN:0263-6484    

DOI:10.1002/cbf.290070102

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA perifusion system was designed in order to study glucose and glutamine metabolism by freshly harvested Ehrlich ascites tumour cells in steady state conditions. Cells were perifused in the presence of 5 mMglucose, 0·5 mMglutamine or 5mMglucose and 0·5 mMglutamine. The results in steady state reveal that both substrates glucose and glutamine are continuously wasted by tumour cells, excreting two moles of lactate per mol of glucose and one mol of glutamate and ammonia per mol of glutamine consumed into the medium. Glutamine consumption in the presence of glucose was higher than with glutamine alon

ISSN:0263-6484    

DOI:10.1002/cbf.290070103

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractChanges in lipid composition and function of subcellular organelles have been described in transplanted and primary tumours. We examine here the fatty acid composition of individual phospholipids (PL) in hyperplastic nodules and primary hepatoma induced by diethylnitrosamine (DEN), compared to that of normal liver and of transplantable Yoshida AH‐130 hepatoma.Phosphatidylcholine and phosphatidylethanolamine fatty acid composition in mitochondria and microsomes from primary hepatoma were markedly different from normal liver; C18:0/C18:1 ratio was lower and the ratio between monounsaturated and polyunsaturated fatty acids was higher. Linoleic acid content of mitochondrial cardiolipin, usually very high in normal rat liver, was notably lower in primary hepatoma. Cholesterol/phospholipid ratio in both microsomes and mitochondria from DEN‐induced hepatoma was higher than in normal liver. Hyperplastic nodules showed no changes in cholesterol content whereas modifications in fatty acid composition were already observeable. These modifications of membrane structure may be related to the functional changes found in nodular cells.Changes in fatty acid composition of membrane phospholipids, occurring in both primary hepatoma and preneoplastic nodules, might be one of the causes for decreased rate of lipid peroxidation peculiar to these tiss

ISSN:0263-6484    

DOI:10.1002/cbf.290070104

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA high percentage of the total tyrosinase found in Harding–Passey mouse melanoma occurs as a soluble form. This paper shows that melanosomal tyrosinase can be solubilized by several endogenous proteases to yield active tyrosinase. This enzyme, once proteolitically solubilized, can be further degraded, leading to enzyme inactivation. The nature and specificity of the main proteases involved in the solubilization process change depending on the size and necrosis stage of the tumour. Cathepsin B could be the main protease responsible for the solubilization in small tumours (<0·5 g). Large tumours are rich in necrotic cells, and cathepsin D and serine‐proteases are the main hydrolytic enzymes involved in the proteolytic action on mealanosomes. These results support the view that the high activity of tyrosinase found in the soluble fraction of malignant melanoma is mainly an artefact resulting from degradation of melanosomes by a variety of endogenous proteases, rather than the result of the actual occurrence of high levels of an independent cytosolic iso

ISSN:0263-6484    

DOI:10.1002/cbf.290070105

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractSpecific binding sites for angiotensin II were localized in the developing rat kidney (18th day of pregnancy and immediately before birth) by autoradiography using [125I]‐ileu‐5‐angiotensin II either perfusedin vivothrough the fetal aorta or addedin vitroto frozen sections in an incubation mixture. Specific binding was localized in the walls of the afferent and efferent arterioles, in the intraglomerular cells and in the peritubular arterioles of the subcapsular cortical zone. The immunohistochemical analysis, carried out on receptors saturated with unlabelled angiotensin II perfused through the mother's aorta, confirmed the autoradiographical localization. Antisera against ileu‐5‐angiotensin II were used in the indirect immunofluorescence technique and in the PAP method. Immunolocalization of angiotensin II was also found in the proximal tubule and in the thick ascending limb of Hen

ISSN:0263-6484    

DOI:10.1002/cbf.290070106

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractTo assess the possibility that atrial natriuretic peptide plays a role in salt and water balance during early mammalian development, we examined hearts from fetal and neonatal rates for the presence of this peptide and presumed target tissues for their ability to bind the hormone. Immunohistochemistry was used to localize and radioimmunoassay to quantify this peptide in heart. Immunoreactive artrial natriuretic peptide was visualized in the fetal heart on day 17·5 post‐conception. It was distributed throughout the atrial appendages and free wall and, in ventricle, in the trabeculae carnae and chordae tendineae. The concentrations of immunoreactive atrial natriuretic peptide in atria of rats on day 19·5 post‐conception were one‐tenth of those in the adult. Levels of this peptide in fetal ventricle were low and virtually absent from the adult tissue. Specific binding of radiolabelled atrial natriuretic peptide measured by whole organ counting occurred in several organs from 19·5‐day fetal and neonatal rats. A number of these tissues, including the kidney, ileum, adrenal, lung and liver, are targets for and/or bind the peptide in adult rats. Specific binding in these tissues was localized using autoradiography at anatomical sites similar to those in adult organs. Specific binding was also seen in fetal but not neonatal skin. In the kidney, binding was associated with immature as well as mature glomeruli. These findings support the proposition that atrial natriuretic peptide may function in the perinatal rat as it does in the adult and, in addition, may play a unique role during

ISSN:0263-6484    

DOI:10.1002/cbf.290070107

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractCharacterization of the phosphate transport system across the basolateral membrane of renal proximal tubule has been attempted using isolated proximal tubule cells prepared from chicks. The Pi efflux system is independent of Na+ions and is not influenced by the nature of the chief anion present in the bathing medium. Pi efflux is not sensitive to DIDS and it is concluded that a generalized anion transporter of band III type is not the chief agent for facilitating Pi exit from the cell across the basolateral membrane. Inhibition of efflux by vanadate is evidence for a specific carrier protein in the membrane. The carrier probably possesses thiol group(s) that are essential for activity. The carrier may effect electroneutral transport of Pi possibly in exchange for OH−ions. The activity of the transport process is not stimulated by depleting the cells of phosphate or inhibited by rearing the chicks on a vitamin D‐deficient diet. The system is unlikely to be of great importance for the expression of various regulatory mechanisms that act on the kidney to control the excretion of Pi. The activity declines as the chicks mature howe

ISSN:0263-6484    

DOI:10.1002/cbf.290070108

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA prostaglandin oligomeric derivative was synthesized by alkaline treatment of prostaglandin E1. This compound protected the perfused rat heart from global ischemia. This compound was found to inhibit several lipolytic and proteolytic enzymesin vitro. When phospholipase A2fromNaja najavenom was used as an enzyme and phosphatidylcholine was used as a substrate, 50 per cent inhibition was achieved at 50 μMof the prostaglandin derivative. When trypsin and casein were used as enzyme and substrate, 50 per cent inhibition was obtained at 80 μM. A possible mechanism of beneficial effect of this compound in protecting membranes during ischemia is discusse

ISSN:0263-6484    

DOI:10.1002/cbf.290070109

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe fate of native alpha 2‐macroglobulin (α2M) or its trypsin complex (α2M‐T) was studied in the isolated dually‐perfused lobule of term human placenta. [125I]‐α2M added to the maternal circuit was unchanged during the course of the perfusion with minimal activity becoming associated with the placental tissue. Transfer of radioactivity into the fetal circulation accounted for only 0·07 per cent of the initial dose after 2 h. In contrast, [125I]‐α2M‐T was rapidly taken up into the placental tissue (nearly 28 per cent of the initial dose during the 2‐h perfusion) and breakdown products were released into both maternal and fetal circulations. At the end of 2 h, radioactivity levels on the fetal side were 13 times higher than those found with the native protein. These indications of a classical receptor‐mediated uptake and breakdown pathway were confirmed in experiments in which the acidotrophic agent chloroquine was added to the maternal circuit prior to the α2M‐T. In the presence of chloroquine, tissue uptake was inhibited and the subsequent release of radioactive degradation products into the fetal circuit was similar to the levels seen with α2M. Incubation of term trophoblast cells at 37°C with [125I]‐α2M‐T revealed over three‐fold greater cell‐associated activity than was found with the native protein. In another series of experiments, a purified microvillous membrane fraction was prepared from term placentae using buffers containing 1 mMiodoacetate. In the presence of this proteolytic enzyme inhibitor, binding studies showed a single class of low affinity receptors for the α2M‐T complex capable of binding 4·8 ± 1·3 (SEM) μg of complex per mg of membrane protein. T

ISSN:0263-6484    

DOI:10.1002/cbf.290070110

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe incubation of human platelets with methylglyoxal and glucose produces a rapid transformation of the ketoaldehyde toD‐lactate by the glyoxalase system and a partial reduction in GSH. Glucose utilization is affected at the level of the glycolytic pathway. No effect of the ketoaldehyde on glycogenolysis and glucose oxidation through the hexose monophosphate shunt was demonstrated. Phosphofructokinase, fructose 1,6 diphosphate (F1, 6DP) aldolase, glyceraldehyde 3‐phosphate dehydrogenase and 3‐phosphoglycerate mutase were mostly inhibited by methylglyoxal. A decrease in lactate and pyruvate formation and an accumulation of some glycolytic intermediates (fructose 1,6 diphosphate, dihydroxyacetone phosphate, 3‐phosphoglycerate) was observed. Moreover methylglyoxal induced a fall in the metabolic ATP concentration. Since methylglyoxal is an intermediate of the glycolytic bypass system from dihydroxyacetone phosphate toD‐lactate, it may be assumed that ketoaldehyde exerts a regulating effect on triose m

ISSN:0263-6484    

DOI:10.1002/cbf.290070111

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY