摘要:

AbstractEntamoeba histolytica, the protozoan parasite causing amoebiasis, is carried by approximately 10% of the world's population although only a minority of carriers of the organism present active clinical symptoms.AlthoughEntamoebaare classified as eukaryotes, the biochemistry of these organisms has a number of unusual facets which are reminiscent of prokaryotes. It has indeed been suggested that these cells represent early evolutionary forms that have been successful in surviving unchanged in the protected environment in which they reproduce (the intestine).Glycolysis inEntamoebalacks several of the typical eukaryotic glycolytic enzymes. The pentose phosphate shunt enzymes are missing completely. Another unusual feature of the glycolytic path is the utilization of PPiinstead of ATP in a number of enzyme reactions e.g. phosphofructokinase.Entamoebais the only eukaryote in which one of these PPiutilizing enzymes, phosphoenolpyruvate carboxytransferase, has been found.The respiratory pathway is also an unusual one.Entamoebaare classified as anaerobes but the cells do have an affinity for oxygen. The oxygen is reduced to water at the end of a respiratory chain which is not well understood but which operates withough cytochromes or mitochondria.The nucleic acid, protein and lipid metabolic pathways have not been well studied and interest has mainly focused on the proteolytic processes of the amoeba which have been implicated in the pathogenic, histolytic behaviour of the parasite. Despite these efforts the mechanism of attack of the parasite and the stimuli that cause it to invade the host are not yet clear. This understandably is the goal of much of the present studies concerningE. histolyticabut the organism also deserves study in its own right as an example of an organism that has an unusual biochemistry and may represent an early stage in the evolution of eukaryotic cells.

ISSN:0263-6484    

DOI:10.1002/cbf.290060202

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractPreparations of rat liver sinusoidal plasma membrane have been tested for their ability to metabolize the hepatotoxin carbon tetrachloride (CCl4) to reactive free radicalsin vitroand compared in this respect with standard preparations of rat liver microsomes. The sinusoidal plasma membranes were relatively free of endoplasmic reticulum‐associated activities such as the enzymes of the cytochrome P450system and glucose‐6‐phosphatase. CCl4metabolism was measured as (i) covalent binding of [14C]‐CCl4to membrane protein, (ii) electron spin resonance spin‐trapping of CCl3· radicals and (iii) CCl4‐induced lipid peroxidation. By all of these tests, purified sinusoidal plasma membranes were found unable to metabolize CCl4.The fatty acid composition of the plasma membranes was almost identical to that of the microsomal preparation and both membrane fractions exhibited similar rates of the lipid peroxidation that was stimulated non‐enzymically by γ‐radiation or incubation with ascorbate and iron. The absence of CCl4‐induced lipid peroxidation in the plasma membranes seems to be due, therefore, to an absence of CCl4activation rather than an inherent resistance to lipid peroxidation.We conclude that damage to the hepatocyte plasma membrane during CCl4intoxication is not due to a significant local activation of CCl4to CCl3·

ISSN:0263-6484    

DOI:10.1002/cbf.290060203

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractInsulin and dexamethasone, usually added to culture media, play an important role in maintaining the survival of functional hepatocytes. Adenine nucleotide concentrations and energy charge values of cultured hepatocytes were determined to investigate the relationship between the beneficial effects of these hormones and the energy status of the cells. The results indicate that insulin and dexamethasone are essential in maintaining the metabolic competence of cultured hepatocytes and that this correlates with the absolute concentration of ATP rather than with the energy charge.

ISSN:0263-6484    

DOI:10.1002/cbf.290060204

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractLiver microsomes have a strong ornithine decarboxylase (ODC) inactivating capacityin vitro. The present results suggest that this may be involved in regulation of ODC activityin vivo: (1) the ODC inactivating capacity of microsomes appears susceptible toin vivomodulation: a single administration of thioacetamide, which induces ODC. also causes a significant increase in the inactivating capacity of the microsomes; (2) under conditions leading to increased microsome‐bound ODC‐inactivating capacity (e.g. liver from thioacetamide‐treated rates versus regenerating liver) ODC displays a greater thermal lability and inactivabilityin vitro.A possible involvement of this microsomal activity in an autoregulatory pathway of ODC is suggested by the fact that it is induced by the administration of polyamines. However, inhibition of ODC activity by α‐difluoromethylornithine does not prevent the increase of the microsomal activity caused by thioacetamide. Thus, polyamine biosynthesis does not appear to be an absolute requirement for induction of the microsomal ODC‐inactivating capacity.The apparent half‐life of ODCin vivo, as evaluated after cycloheximide administration, does not appear to correlate with the microsomal ODC‐inactivating capacity content and the stability properties

ISSN:0263-6484    

DOI:10.1002/cbf.290060205

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractWhen Ehrlich ascites tumour cells are induced to proliferate by serum stimulation, the ornithine decarboxylase (ODC) activity increases rapidly and reaches two to three peaks during the first 24 h. Inhibition of the first peak in ODC activity (occurring at 4 h) by adding α‐difluoromethylornithine (DFMO) within 2 h of serum stimulation, results in maximal growth inhibition. Under these conditions, similar degrees of polyamine depletion are achieved. When DFMO is added 3 h after seeding, however, enough polyamines have already accumulated during the initial burst in ODC activity to reduce the antiproliferative effect of the drug. The antiproliferative effect is further reduced when DFMO is added 6 h after seeding. When DFMO is added 23 h after seeding, i.e. after maximal accumulation of polyamines, there is no inhibition of cell proliferation. These findings are important to consider both when designing experimental as well as clinical regimens for this dr

ISSN:0263-6484    

DOI:10.1002/cbf.290060206

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe antileukemic and anti‐HTLV‐III (anti‐HIV) agent avarol, a sesquiterpenoid hydroquinone, was determined to be converted into its corresponding quinone derivative avarone via the semiquinone free radical. Itsg‐value was 2·0047; after hyperfine splitting the energy levels revealed 16 isotropic Hfs. The redox reaction products were identified at the pH values 4·0, 7·0 and 12·0 and the overall reaction pathways were formulated.In vivoexperiments with L5178y mouse lymphoma cells in the ascites of mice revealed that the cytostatic potencies of avarol and avarone cannot be augmented by lowering the pH value. Incubation studies with L5178y cellsin vitroshowed that the intracellular levels of superoxide dismutases (SODases) and of glutathione (GSH) peroxidase activities significantly change after avarol administration. While both the Mn‐SODase and the Cu/Zn‐SODase activities dropped significantly, the GSH peroxidase activity increased inversely. From these experiments we assume that the anti‐tumour and the antiviral effects of avarol/avarone may be due to an increase, induced by the drug, of the intracellular concentrations of su

ISSN:0263-6484    

DOI:10.1002/cbf.290060207

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn crude membrane fractions of rat pancreatic islets and of RIN‐A2‐cells, forskolin and NaF stimulated adenylate cyclase activity. Basal and stimulated enzyme activity was approximately 3 to 6 fold higher in membranes of RIN‐A2‐cells than in membranes of islet cells. In RIN‐A2‐cells GppNHp and NEM inhibited forskolin‐stimulated cyclase system of RIN‐A2‐cells contains inhibitory and stimulatory N‐proteins and that there are critical thiols related to Ni, Nsand/or the catalytic unit. Thus, membrane fractions of RIN‐A2‐cells may be an appropriate model for studies on the adenylate cyclase system of

ISSN:0263-6484    

DOI:10.1002/cbf.290060208

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe distribution of intestinal transglutaminase was investigated by immunofluorescence microscopy using rabbit anti‐guinea pig transglutaminase immunoglobulin. Transglutaminase‐related antigen was demonstrated principally in the cytoplasm of villous core interstitial cells with some activity in the brush border region of the villous epithelial cells. Implications for the pathogenesis of coeliac disease are discus

ISSN:0263-6484    

DOI:10.1002/cbf.290060209

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290060211

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290060213

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY