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PubMed1997

Isolation and partial characterisation of insulin-mimetic inositol phosphoglycans from human liver.

Extracts of human liver were found to contain activities which copurified and coeluted with the two major subtypes of mediators (type A and type P) isolated from insulin-stimulated rat liver. The putative type A mediator from human liver inhibited cAMP-dependent protein kinase from bovine heart, decreased phosphoenolypyruvate carboxykinase mRNA levels in rat hepatoma cells, and stimulated lipogenesis in rat adipocytes. The putative type P mediator stimulated bovine heart pyruvate dehydrogenase phosphatase. Both fractions were able to stimulate proliferation of EGFR T17 fibroblasts and the type A was able to support growth in organotypic cultures of chicken embryo cochleovestibular ganglia. Both activities were resistant to Pronase treatment and the presence of carbohydrates, phosphate, and free-amino groups were confirmed in the two fractions. These properties are consistent with the structure/ function characteristics of the type A and P inositolphosphoglycans (IPG) previously characterized from rat liver. Further, the ability of the human-derived mediators to interact with rat adipocytes and bovine-derived metabolic enzymes suggests similarity in structure between the mediators purified from different species. Galactose oxidase-susceptible membrane-associated glycosylphosphatidylinositols (GPI) have been proposed to be the precursors of IPG. GPI was purified from human liver membranes followed by treatment with galactose oxidase and reduction with NaB3H4. Serial t.l.c. revealed three radiolabeled bands which comigrated with the putative GPI precursors found in rat liver. These galactose-oxidase-reactive lipidic compounds, however, were only partially susceptible to hydrolysis with phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis and were resistant to glycosylphosphatidylinositol-specific phospholipase C from Trypanosoma brucei. These data indicate that IPG molecules with insulin-like biological activities are present in human liver.

Adult↗
PubMed1982

Properties of hexosaminidases in cell-free extracts of rainbow trout livers and effects of thyroid hormones.

1. The kinetic and physical properties of hexosaminidase (EC 3.2.1.30) activity were studied in liver extracts of juvenile rainbow trout. 2. Differential centrifugation studies failed to unequivocally demonstrate the sub-cellular localization of hexosaminidase, but indicated that the hexosaminidase activity was associated with the mitochondrial and lysosomal fractions. 3. Cell-free, Triton X-100 liver extracts indicated a pH optimum and activation energies comparable to those of mammals, but for other properties trout hepatic hexosaminidase differed markedly from its mammalian counterpart. 4. In contrast to the situation in rats, trout hexosaminidase was uninfluenced by a wide range of T4 and T3 doses administered by either injection or immersion routes. 5. T4 administration increased plasma T4 with minor change in plasma T3, indicating inhibition of T4 to T3 conversion by high T4 levels.

Acetylglucosaminidase↗
PubMed1995

Electrical properties of extracted rat liver tissue.

We attempted to investigate the process of ischemia-induced disturbances in the rat liver, employing the electrical bio-impedance technique. The electrical bio-impedance was measured continuously over 6 h by the 4-electrode method, at various incubation temperatures, in six liver samples extracted from male Wistar rats. The electrical properties of biological tissues can be expressed in terms of three parameters: extracellular resistance (Re), intracellular resistance (Ri) and cell membrane capacitance (Cm). These three parameters were calculated from the measured values of the electrical impedance by the curve-fitting technique, using a computer program. The Re value increased rapidly after the rat livers were extracted, and then decreased slowly. The Re value reached a peak after about 13 min at 36 degrees C, and then decreased slowly, becoming constant after 3 h. There was a negative correlation between the Tmax of Re (the time when Re reached a maximum) and the incubation temperature (R = -0.973, P < 0.001). The Ri value decreased once in the early stage after extraction, followed by almost no change and then an increase after 4 h at 36 degrees C. The Cm showed a similar pattern of change to the Re value, and a negative correlation was also found between the Tmax of Cm and the incubation temperature (R = -0.969, P < 0.001). The increase in the Re and Cm values, and the decrease in the Ri value for quite long periods after the blood flow has stopped, suggest an increase in the resistance of extracellular fluid due to a decrease in its volume, an increase in cell membrane capacitance due to cell swelling, and a decrease in cellular fluid resistance due to an increase in its volume. The time when the Cm value decreases rapidly after an initial gradual decrease after the peak corresponds well with the time when the Ri value begins to increase, from which it is estimated that cell lysis proceeds and that the flow of extracellular fluid into the cell begins at this time. The findings of this study suggest the possibility of estimating the changes in liver tissue or the tissue structure due to ischemia.

Animals↗
PubMed1975

Mutagenic activity of cyclophosphamide, ifosfamide, and trofosfamide in different genes of escherichia coli and salmonella typhimurium after biotransformation through extracts of rodent liver.

Experiments are performed to compare the mutagenic properties of the three phosphamide esters of nitrogen mustard, cyclophosphamide (CP), ifosfamide (IF), and trofosfamide (TF), in different bacterial systems. The systems include forward mutations leading to resistance against 5-methyltryptophan (MTR) and from galR-s18 to gal-+ in Escherichia coli 343/113, back mutations from arg56 to arg-+ in Escherichia coli 343/113 and back mutations from hisG46 to his-+ in Salmonella typhimurium TA1535. CP, IF, and TF are not mutagenic per se. After biotransformation through isolated rodent liver homogenates (S-9 fraction) all three compounds exhibit mutagenic activity in the order CP smaller than IF smaller than TF. Specific activating potential of mouse liver extracts is higher than that of rat liver. Except for back mutations in S. typhimurium TA1535, all mutation systems tested show a similar pattern of induction after treatment with CP, IF, and TF. However, because gal-+ mutations are not induced by CP under conditions where arg-+ and MTR are induced, it is suggested that more than one mutational system be used in routine mutagenicity testing.

Animals↗
PubMed1979

The decarboxylation of S-adenosylmethionine by detergent-treated extracts of rat liver.

1. The production of (14)CO(2) from S-adenosyl[carboxyl-(14)C]methionine by rat liver extracts was investigated. It was found that, in addition to the well-known cytosolic putrescine-activated S-adenosylmethionine decarboxylase, an activity carrying out the production of (14)CO(2) could be extracted from a latent, particulate or membrane-bound form by treatment with buffer containing 1% (v/v) Triton X-100 [confirming the report of Sturman (1976) Biochim. Biophys. Acta428, 56-69]. 2. The formation of (14)CO(2) by such detergent-solubilized extracts differed from that by cytosolic S-adenosylmethionine decarboxylase in a number of ways. The reaction by the solubilized extracts did not require putrescine and was not directly proportional to time of incubation or the amount of protein added. Instead, activity a showed a distinct lag period and was much greater when high concentrations of the extracts were used. The cytosolic S-adenosylmethionine decarboxylase was activated by putrescine, showed strict proportionality to protein added and the reaction proceeded at a constant rate. Cytosolic activity was not inhibited by homoserine or by S-adenosylhomocysteine, whereas the Triton-solubilized activity was strongly inhibited. 3. By using an acetone precipitate of Triton-treated homogenates as a source of the activity, it was found that decarboxylated S-adenosylmethionine was not present among the products of the reaction, although 5'-methylthioadenosine and 5-methylthioribose were found. Such extracts were able to produce (14)CO(2) when incubated with [U-(14)C]-homoserine, and (14)CO(2) production was greater when S-adenosyl[carboxyl-(14)C]methionine that had been degraded by heating at pH6 at 100 degrees C for 30min (a procedure known to produce mainly 5'-methylthioadenosine and homoserine lactone) was used as a substrate than when S-adenosyl[carboxyl-(14)C]methionine was used. 4. These results indicate that the Triton-solubilized activity is not a real S-adenosylmethionine decarboxylase, but that (14)CO(2) is produced via a series of reactions involving degradation of the S-adenosyl-[carboxyl-(14)C]methionine. It is probable that this degradation can occur via several pathways. Our results would suggest that part of the reaction occurs via the production of S-adenosylhomocysteine, which can then be converted into 2-oxobutyrate via the transsulphuration pathway, and that part occurs via the production of homoserine by an enzyme converting S-adenosylmethionine into 5'-methylthioadenosine and homoserine lactone.

Adenosylmethionine Decarboxylase↗
PubMed1980

Stimulation of hepatic regeneration after partial hepatectomy by infusion of a cytosol extract from regenerating dog liver.

A cytosol liver extract was prepared from adult dog livers and from liver remnants that had been regenerating for one, two and three days after 72 per cent partial hepatectomy. Given intraportally, the most active of these cytosols did not stimulate proliferation in the livers of normal dogs. However, infused during a six hour period into the portal vein of test group dogs, the cytosol from 48 and, especially, 72 hour regenerating livers augmented the regeneration response ordinarily produced by 44 per cent partial depatectomy. The effect was delayed. It became identifiable 48 hours after infusion and rached a peak at 72 hours. Neither augmentation nor significant inhibition of the normal regeneration response was produced by cytosol from normal liver and 24 hour regenerating liver or by six hour infusion of insulin. The amplification effect of active cytosol was equivocal when the infusions were given intraperitoneally and was not demonstrable at all by the intravenous route. In these investigations, it is confirmed that there are growth control factors in regenerating liver but the nature or physiologic significance of the factor or factors has not been clarified.

Animals↗
PubMed1987

Alterations in the sensitivity to endogenous proteolysis due to storage of fructose-1,6-bisphosphatase extracts of liver and muscle of young and old rats.

The sensitivity of fructose-1,6-bisphosphatase (FBPase: EC 3.1.3.11) to endogenous proteolysis was studied in liver and muscle extracts of young (28 weeks) and old (97 weeks) rats (stored at 4 degrees +/- 2 degrees C) by monitoring the alterations in its properties. Apart from the level of total enzyme activity, decrease in activity ratio (at pH 7.0/9.2) and sensitivity to AMP inhibition no age-dependent significant change was found during storage of the liver extract. However, a more significant increase in activity, comparatively less decrease in activity ratio, and retention of sensitivity to AMP inhibition were observed during the storage of muscle enzyme extract from old rats than from young rats. Using gel electrophoresis, an extra degradative active product was observed in all samples except those of old rat muscle. These results may indicate tissue-specific alterations in the susceptibility of FBPase to endogenous proteolysis during old age in the rat.

Aging↗
PubMed1976

Properties of hepatic tissue extracts: 2. An approach to the artificial liver.

In the previous paper [3], the lethal effect of normal rabbit liver extract intravenously infused into rabbits was described. By comparing to the course of destruction of the liver tissue in fulminant hepatitis, the toxicity of the liver extract was recently studied. Attempts were also made to adsorbing the liver extract by activated clay and detoxifying the liver extract with a formaldehyde solution, and the results suggested that the findings would be applicable as an approach to the artificial liver.

Adsorption↗
PubMed1999

DNA-protein interactions in the CCAAT box region of the murine lactate dehydrogenase C promoter.

Electrophoretic Mobility (EMSA), using oligonucleotides containing CCAAT box sequences from the murine Idhc promoter show the presence of CCAAT binding proteins in nuclear extracts from liver and testis. In a liver extract, a single shifted band is seen. However, in the testis extract, two shifts are observed, one of which may be due to a testis specific isoform of CCAAT binding factor (CBF). Southwestern analysis with an oligonucleotide probe containing these sequences reveals the presence of a protein of approximately 120 kD in the testis extract. In the liver extract, a 70-kD protein binds the probe. An antibody against HeLa CBF causes a supershift in testis nuclear extract.

Animals↗
PubMed1982

The nature of hepatic lymphocytic infiltrates in the tropical splenomegaly syndrome.

The lymphocytes infiltrating the liver of patients with tropical splenomegaly syndrome (TSS) were shown to be mainly T lymphocytes. Migration of leucocytes obtained from patients with TSS was inhibited by TSS liver extract, normal liver extract and liver-specific lipoprotein. These findings suggest that the hepatic infiltrates which occur in TSS are probably caused by a cell-mediated immune response to an antigen present in liver cells.

B-Lymphocytes↗
PubMedDate not supplied

Extraction and analysis of superoxide free radicals (.O2-) from whole mammalian liver.

Extraction of whole lobes of normal rat liver with dimethyl sulphoxide (DMSO) under N2 gives extracts which contain 5-10 mumol/l.O2- (50-100 nmol.O2- per 10 ml extract per 4 g liver; 1.25-2.50 nmol.O2- per millilitre per gram liver). Evidence for .O2- in the extracts is given by: (1) electron spin resonance signals (ESR), (2) differential pulse polarography (DPP), (3) chemiluminescence (CL), and (4) nitroblue tetrazolium reduction (NBT). All tests yield results identical with those obtained with authentic .O2-. Extraction of .O2- is enhanced by tetrabutyl ammonium ion, and is maximal at 1-3 min. These results raise the possibility that substantial amounts of .O2- are normally sequestered in protective membranous sites in vivo.

Animals↗
PubMed1979

Identification and partial purification of an ATP-stimulated alkaline protease in rat liver.

Extracts from rat liver contain a sulfhydryl-dependent endoprotease which degrades [methyl-14C]globin or 125I-hemoglobin to acid-soluble peptides. This enzyme was isolated from the 100,000 x g supernatant of the homogenate. It showed a pH optimum between 7.5 and 9.5 and very little activity below pH 7.0. The enzyme has an apparent molecular weight of 550,000 as determined on Sepharose 6B column chromatography and sucrose density gradient centrifugation. ATP, at physiological concentrations, as well as pyrophosphate, stimulated the protease activity in these partially purified preparations up to 3-fold. Nonionic detergents such as Triton X-100 increased proteolytic activity and the stimulation by ATP. Other nucleotide triphosphates and ADP also increased proteolysis but less effectively than ATP. Sodium phosphate, creatine phosphate, and EDTA had no stimulatory effect.

Adenosine Triphosphate↗