摘要:

AbstractMouse hepatocytes from healthy control mice and from Ehrlich ascites tumour‐bearing mice were used for tracer‐kinetic studies of purine catabolism of liver cells during different periods of tumour growth. The dynamics of the radioactive tracers were modelled mathematically by a system of differential equations. Computer simulations, i.e. direct fitting of numerical solutions of these equations to the observed time‐courses of metabolites and specific radioactivites, enables one to estimate unknown kinetic parameters of a simplified model of pathways of hepatic purine catabolism in tumour‐bearing mice.There occurred great differences of metabolic flux rates between control hepatocytes, hepatocytes of mice during the proliferating period of tumour growth (6th day after inoculation of the tumour) and hepatocytes of mice during the resting period of tumour growth (12th day after inoculation of the tumour). The final purine degradation of hepatocytes prepared during the proliferating period was lower in comparison with that of control hepatocytes, but it was markedly higher in hepatocytes prepared during the resting period of tumour growth. The changes in hepatocyte purine catabolism during the proliferating period of tumour growth argue for transitions which aim at the maintenance of high purine nucleotide levels in the liver itself rather than for an increased nucleoside and nucleobase supply for the tumour. This suggestion is in accordance with the increased ATP level of the liver during the proliferating phase of tumour growth. The drastic acceleration of the final steps of hepatic purine catabolism forming uric acid and allantoin during the resting period of tumour growth was predominantly due to increased flux rate from xanthosine and guanine in accordance with increased catabolism of monophosphorylated nucl

ISSN:0263-6484    

DOI:10.1002/cbf.290120102

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe characteristics of the enzyme γ‐glutamyltranspeptidase were determined in frog liver and compared to those of the rat. InRana pipiens, tissue distribution studies indicated the order of activity to be: kidney>>>liver>>nerve>egg>lung>heart>skeletal muscle in homogenates. In theRana pipiensrelative to the Fischer 344 rat, the activity of the liver enzyme was somewhat greater (1·8‐fold) and the kidney enzyme substantially less (25‐fold). Frog liver γ‐glutamyltranspeptidase displayed strain‐dependent differences in activity withRana pipiensandRana sylvaticaexhibiting comparable activities andXenopus laevisexhibiting 20‐fold lower activities. No influence of sex was apparent inRana pipiensin contrast to the sex dependent differences observed in the Fischer 344 rat: ♀ : ♂ = 7:1. In homogenates and plasma membrane fractions ofRana pipiens, Xenopus laevisand the Fischer 344 rat, high, and comparable relative specific activities, were observed, 8–11, coupled with protein yields of 2·2–2·5 per cent indicating the enzyme to be plasma membrane bound and associated with the sinusoidal surface of the liver cell. Both the frogRana pipiensandXenopus laevisand Fischer 344 rat liver plasma membrane enzymes displayed comparable temperature‐induced activation (1·51–1·74‐fold) but with a peak for the frogs at 60°C and for the rat at 50°C. Both Acivicin and maleate inhibited the liver plasma membrane γ‐glutamyltranspeptidase of bothRana pipiensand the Fischer 344 rat, but the frog enzyme was less sensitive (89 per cent decrease versus 97 per cent decrease) to 150 μM Acivicin and more sensitive (65 per cent decrease versus 35 per cent decrease at 150 mM maleate) to maleate. Kinetic studies indicated that the liver plasma membrane enzyme fromRana pipienshad aKmof 0·61 mM andVmaxof 55·6 nmol mg−1min−1and that from the Fischer 344 rat had

ISSN:0263-6484    

DOI:10.1002/cbf.290120103

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractEnalapril maleate (EM) is the salt ofN‐{(S)‐1‐(ethoxycarbonyl)‐3‐phenylpropyl}‐L‐alanyl‐L‐proline, used therapeutically as an anti‐hypertensive agent. The effects of EM on some aspects of the energy metabolism and membrane properties of mitochondria from rat liver and kidney cortex were studied, but only the latter were significantly affected. With 0·8 mMof EM and 2‐oxoglutarate as oxidizable substrate for isolated mitochondria from rat kidney cortex, the findings were: (a) inhibition of the respiratory rate in state III (37 per cent) and decrease (45 per cent) in respiratory control ratio (RCR), with only one addition of ADP; (b) reinforcement of the inhibition when a second addition of ADP was made; (c) no significant effect either on the rate of respiration in state IV or on the ADP/O ratio; (d) no effect on the ATPase activity of mitochondria from liver or kidney cortex; (e) inhibition of the transmembrane potential (Δψ) after a second addition of ADP; (f) inhibition of the 2‐oxoglutarate dehydrogenase complex. It is suggested that in kidney mitochondria, EM interferes in the gluconeogenesis dependence of at least five substrates: 2‐oxoglutarate, glutamine, glutamate, lactate, and pyruvate. Also EM may inhibit Na+/H+

ISSN:0263-6484    

DOI:10.1002/cbf.290120104

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA method for preparing various forms of acetylcholinesterase (A ChE) from chicken brain has been developed and they have been characterized in terms of kinetic parameters such asKm, rate constant (k), turnover number (kp), specificity constant (ksp),Vmaxand half‐life (t1/2). The solubility experiments show that, there are two major forms of A ChE i.e. water‐soluble and membrane‐bound A ChE (MBA ChE). The MBA ChE shows several subforms, and on the basis of percentage activity only three MBA ChE forms have been selected for complete characterization by various kinetic parameters. It was found that these three forms of MBA ChE demonstrate significant differences in their kinetic prope

ISSN:0263-6484    

DOI:10.1002/cbf.290120105

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMost of the DNA polymerase α activity, bound to the heat‐stabilized nuclear matrix prepared from HeLa S3 cells, was released as a matrix extract by sonication. When the extract was centrifuged in a 5–20 per cent linear sucrose gradient no definite peaks of activity could be identified. Most of the activity sedimented to the bottom of the tube under all the conditions tested, whilst the remaining activity was associated with matrix fragments of various and irregular size. No 10 S complexes, containing polymerase activity, were seen after incubation of the extract for 16 h before centrifugation. Other solubilization procedures (i.e. treatment of the matrix with chelating agents, high pH associated with reducing agents, ionic and nonionic detergents) failed to produce release of matrix‐bound DNA polymerase α activity. In contrast, we released 10 S complexes, containing polymerase activity, from the matrix prepared from nuclei not exposed to heat. We conclude that a 37°C incubation of isolated nuclei before extraction with 2 M NaCl and DNase I digestion causes DNA polymerase α to bind to the nuclear matrix in a form that cannot subsequently be released as discrete components, at variance with previous results obtained with the matrix prepared from regenerating

ISSN:0263-6484    

DOI:10.1002/cbf.290120106

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA previous study showing that ethanol (ETOH) blocked [3H]choline incorporation into phosphatidylcholine (PC) suggested an inhibition of PC biosynthesis in human leukemic monocyte‐like U937 cells. The mechanism of the inhibitory action of ETOH was investigated. Cells were pulsed with [3H]choline for 30 min and chased in the presence or absence of ETOH for up to 6 h. PC biosynthesis was inhibited drastically within 1 h after exposure to ETOH which increased intracellular cAMP appreciably. After a 3‐h treatment, ETOH significantly inhibited both choline kinase (CK) and the cytosolic CTP: cholinephosphate cytidylyltransferase (CT). The inactivated CT was no longer stimulated by exogenous phosphatidylglycerol (PG). There was no evidence for redistribution of CT activity between cytosol and microsomes. When cells were exposed to 8‐Bromo‐cAMP ranging from 100 to 300 μM, PC biosynthesis remained unaffected despite the drastically elevated cAMP. These results seem to suggest that the raised cAMP is not a prerequisite for the inhibition of PC biosynthesis in U937 cells. Following pretreatment with protein kinase inhibitors (H‐89 and K‐252a), PC biosynthesis was decreased significantly and the inhibitory effect of ETOH was potentiated. Taken together, our results suggest that the inhibition of PC biosynthesis and the inhibitory effect of ETOH are independent of the activation of cAMP‐dependent protein kinase. Unlike protein kinase inhibitors, pretreatment with tyrosine kinase inhibitors (erbstatin, genistein and tyrphostin 25) resulted in differential effects on PC biosynthesis and on the inhibitory action of ETOH. Genistein stimulated PC biosynthesis by 30 per cent as well as partially preventing /reversing the ETOH action, while tyrphostin 25 produced a synergistic inhibition. The relevance of tyrosine phosphorylation/dephosphorylation to the regulation of PC biosynthesis and ETOH action remains to

ISSN:0263-6484    

DOI:10.1002/cbf.290120107

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract4‐Hydroxynonenal (HNE) is produced during peroxidation of polyunsaturated fatty acids. It exerts a chemokinetic effect on human polymorphonuclear leukocytes (PMN). Investigations of this mechanism were performed. The results indicate that [3H]‐HNE binding to PMN results both in non‐specific bonds to the numerous SH groups of the cells and in binding to a saturable, reversible and specific HNE site. Scatchard analysis revealed that this is a single site with an apparent affinity constant of 319 nM and a density of 1·57 pmol (106)−1cells. This specific binding site may be involved in the chemokinetic effec

ISSN:0263-6484    

DOI:10.1002/cbf.290120108

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNew drugs are generally developed against animal models of the human disease. Before they are subjected to clinical trials it might be helpful to be able to test whether they are as effective against the disease in human tissue as they were in animals. It is proposed that this can be achieved by the use of organ maintenance culture of the human diseased tissue, the relevant biochemical parameters being measured by quantitative cytochemistry. In the present studies differences between the effect of indomethacin and of the ‘chondroprotective’ drug diclofenac sodium, on human osteoarthritic cartilage, have been measu

ISSN:0263-6484    

DOI:10.1002/cbf.290120109

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRat hearts were perfused with the Langendorff technique at constant flux in the presence of the oxidizing agents hydrogen peroxide and diamide. Fructose 1,6‐bisphosphate strongly prevented the decline of heart contractility due to the infusion of these oxidizing agents. On the other hand, fructose 1,6‐bisphosphate had no effect on the release of total glutathione into the perfusate but prevented the loss of lactate dehydrogenase indicating a protective effect on cell membranes. Comparing the cytosolic and mitochondrial loss of glutathione, fructose 1,6‐bisphosphate exerted a beneficial action only on the mitochondrial fraction. Several mechanisms of action have been considered to explain the protective action of frutose 1,6‐bisphosphate. In our experimental conditions fructose 1,6‐bisphosphate might stimulate its own production giving rise to dihydroxyacetone phosphate, that, after reduction to glycerol 3‐phosphate, can permeate the mitochondrial membrane with the final productio

ISSN:0263-6484    

DOI:10.1002/cbf.290120110

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290120113

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY