Polyamine synthesis during lymphocyte activation : Induction of ornithine decarboxylase and S-adenosyl methionine decarboxylase

Lymphocyte stimulation by phytohaemagglutinin (PHA) is accompanied by marked increases in the activities of ornithine decarboxylase and S-adenosyl methionine decarboxylase, two key enzymes for the synthesis of polyamines. Both enzymes increase in a biphasic manner, with the rises in S-adenosyl methionine decarboxylase preceding the increases in ornithine decarboxylase. The initial rises precede the initiation of DNA synthesis, and seem to correlate with the increased rate of ribosomal RNA synthesis. Selective inhibition of ribosomal RNA synthesis inhibits the increases in the activity of both enzymes, especially ornithine decarboxylase, more than the increase in the overall rate of protein synthesis.Both enzymes are metabolically unstable and have half-lives of less than 1 h, although the half-life of ornithine decarboxylase depends on the amino acid concentration in the culture medium. While effects of PHA on the stability of the enzymes have not been ruled out, at least part of the PHA-dependent increases in activity are due to increased synthesis or activation of the enzymes. The synthesis of S-adenosyl-methionine decarboxylase declines rapidly after inhibition of RNA synthesis, but ornithine decarboxylase activity declines at about the same rate as protein synthesis as a whole.The activities of both enzymes also increase during lymphocyte stimulation by concanavalin A, lentil extract and staphylococcal filtrate.     

Subcellular localization of superoxide dismutase in rat liver.

The subcellular localization of superoxide dismutase was investigated in rat liver homogenates. Most of the superoxide dismutase activity is present in the soluble fraction (84%), the rest being associated with mitochondria. No indications for the occurrence of superoxide dismutase in other subcellular structures, particularly in peroxisomes, was found. Mitochondrial activity is not due to adsorption, since the sedimentable activity is essentially latent. Subfractionation of mitochondria by hypo-osmotic shock and sonication shows that half of the mitochondrial superoxide dismutase activity is localized in the intermembrane space, the rest of the enzyme being a component of the matrix space. In non-ionic media the matrix enzyme is, however, adsorbed to the inner membrane, from which it can be desorbed by low (0.04M) concentration of KCl. Superoxide dismutase activity was found in all rat organs investigated. Maximal activity of the enzyme is observed in liver, adrenals and kidney. In adrenals, the highest specific activity is associated with the medulla.     

Subcellular localization of ornithine decarboxylase in liver of control and growth-hormone-treated rats.

1. Ornithine-2-oxo acid aminotransferase activity was inhibited by amino-oxyacetate (10(-5) M). This permitted the measurement of ornithine decarboxylase in the presence of mitochondria by using the 14CO2-trapping technique. 2. Subcellular fractionation of rat liver by differential centrifugation, followed by the assay of ornithine decarboxylase in the presence of amino oxyacetate and of marker enzymes for each fraction, demonstrated that ornithine decarboxylase was located in the cytosol. 3. The greatly increased ornithine decarboxylase activity observed after growth-hormone administration was also found to be localized in the cytosol. 4. The Km of ornithine decarboxylase from rat liver for ornithine was 28 muM. Administration of growth hormone 4 h before death did not affect the apparent affinity of ornithine decarboxylase for ornithine.     

Chronic ethanol feeding causes oxidative stress in rat liver mitochondria. Prevention by S-adenosyl methionine

Oxygen utilisation during tyrosinase-catalysed oxidation of 4-hydroxyanisole was investigated using an electron spin resonance technique which employs quantitative changes in the characteristics of the electron spin resonance spectrum of the spin label 3-carbamoyl-2,5-dihydro-2,2,5–5-tetramethyl-1-H-pyridoyl-1-yloxy (CTPO) to follow changes in the oxygen concentration. Reaction mixtures containing mushroom tyrosinase (15 μg ml^?1) and differing initial concentrations of 4-hydroxyanisole in aerated phosphate buffer at pH 6.8 were incubated at room temperature. The ratio of utilisation of oxygen was found to be in approximately 1:1 molar ratio with the initial 4-hydroxyanisole concentration in the reaction mixture between 50 and 200 μmol/1 4-hydroxyanisole. The results are consistent with the stoichiometry of oxygen utilisation being accounted for by the oxidation of 4-hydroxyanisole to anisyl quinone.     

Subcellular localization of a membrane-associated transglutaminase activity in rat liver

Fractionation of rat liver by homogenization and differential centrifugation revealed that only about 83% of the transglutaminase activity in the tissue is in a soluble form, and that the remainder is associated with the particulate fraction. This latter activity remained with the membranes even after they were extensively washed to remove 99% of such soluble enzymes as lactate dehydrogenase and aldolase. Subsequent fractionation of the membranes by isopycnic density gradient centrifugation in sucrose resulted in a single band of transglutaminase activity at a density of 1.194 g/cm3. This activity was coincident with the major band of plasma membranes, which was identified by its content of 5'-nucleotidase, alkaline phosphodiesterase I, alkaline phosphatase and leucine aminopeptidase activities. After treatment with digitonin and fractionation on sucrose gradients, the transglutaminase activity and the plasma membrane marker enzyme activities were found at a new density of 1.210 g/cm3, while the enzyme markers for the other membrane fractions remained unchanged. From these data, we conclude that approximately 17% of the transglutaminase activity in rat liver is specifically associated with the plasma membranes.     

Subcellular localization of low-molecular-weight RNA components in rat liver.

The subcellular localization of the four major low-molecular-weight RNA components, D, C, A and L, was studied in rat liver cells. The cells were fractionated by a non-aqueous technique into a nuclear and a cytoplasmic fraction. The cytoplasm contained 43% of component D, 57% of component C and more than 80% of component L.     

腺苷蛋氨酸预防酒精性肝病及其作用机制探讨

目的探讨腺苷蛋氨酸(SAM)防治大鼠酒精性肝病的作用机制。方法健康雄性wistar大鼠30只,随机分为对照组、模型组和SAM干预组。模型组大鼠采用逐渐增加浓度(30%-60%)和剂量(5-9g·kg-1·d-1)的方法酒精灌胃16周,干预组增加SAM(100mg/kg)灌胃,其它同模型组。16周末随机处死动物,检测血清总同型半胱氨酸(tHcy)的浓度和肝组织胱硫醚β合成酶(CBS)的活性;分别采用免疫组化方法和RT-PCR法检测肝组织中GRP-78、calpain 2及其caspase-12的表达;采用TUNEL染色法检测肝细胞凋亡。结果模型组大鼠16周末出现肝细胞弥漫小泡性脂肪变性,窦周纤维化,汇管区纤维组织增生并有纤维间隔形成。SAM组病理改变较模型组明显减轻。SAM组血清tHcy的浓度(7.00±0.79)较模型组(9.85±0.12)明显降低,而CBS的活性(511.60±57.44)较模型组(390.45±31.17)升高,F值分别为147.28和41.14,P值均<0.01;免疫组化和RT-PCR结果显示SAM组GRP-78、Calpain 2、caspase-12的表达较模型组减弱;SAM组的肝细胞凋亡指数(31.24±2.65)较模型组(65.71±9.78)降低,F值为301.79,P<0.01。结论在大鼠酒精性肝病中,腺苷蛋氨酸通过提高胱硫醚β合成酶活性,改善内质网应激,减少肝细胞凋亡,减轻肝脏损伤。     

Subcellular localization of B apoprotein of plasma lipoproteins in rat liver

Multispecific antigen-binding fragments (Fab) from rabbit antisera against rat very low density lipoproteins (VLDL) and Fab against rat low density lipoproteins that were monospecific for the B apoprotein were conjugated to horseradish peroxidase. Conjugates were incubated with 6-mum frozen sections from fresh and perfusion-fixed livers and with tissue chopper sections (40 mum thick) from perfusion-fixed livers. In the light microscope, specific reaction product was present in all hepatocytes of experimental sections as intense brown to black spots whose locations corresponded to the distribution of the Golgi apparatus: along the bile canaliculi, near the nuclei, and between the nuclei and bile canaliculi. Perfusion fixation with formaldehyde produced satisfactory ultrastructural preservation with retention of lipoprotein antigenic determinants. In the electron microscope, patches of cisternae and ribosomes of the rough endoplasmic reticulum (ER) and particularly its smooth-surfaced ends, vesicles located between the rough ER and the Golgi apparatus, the Golgi apparatus and its secretory vesicles and VLDL particles in the space of Disse all bore reaction product. The tubules and vesicles of typical hepatocyte smooth ER did not contain reaction product, nor did the osmiophilic particles contained therin. The localization obtained in this study together with other evidence suggests a sequence for the biosynthesis of VLDL that differs in some respects from that proposed by others: (a) the triglyceride-rich particle originates in smooth ER where triglycerides are synthesized; (b) at the junction of the smooth and rough ER the particle receives apoproteins synthesized in the rough ER; (c) specialized tubules transport the particle, now a nascent lipoprotein, to the Golgi apparatus where concentration occurs in secretory vesicles; (d) secretory vesicles move to the sinusoidal surface where the particles are secreted into the space of Disse by fusion of the vesicular membrane with the plasma membrane of the hepatocyte.     

Subcellular localization and properties of rat liver adenosine diphosphatase.

ADPase (adenosine diphosphatase) was assayed in rat liver homogenates with [beta-32P]ADP as substrate. The activity had a pH optimum of 8.0 and was strongly activated by Mg2+. The intracellular localization was determined by analytical subcellular fractionation with single-step sucrose-density-gradient centrifugation. Selective membrane perturbants were used to enhance the resolution of the various organelles. ADPase was localized to the mitochondria. Mitochondria were isolated by differential centrifugation and subfractionated by selective disruption of the inner and outer membranes. The intramitochondrial localization of ADPase was compared with various marker enzymes and was shown to be concentrated in the outer-membrane fractions. The effects of various inhibitors on the ADPase activity were determined and the possibility that the activity could be due to known enzyme systems was considered. It is concluded that ADP degradation is due to a hitherto unrecognized mitochondrial enzyme.     

Subcellular localization of acid carboxypeptidase in rat liver and human fibroblasts.

The subcellular distribution of acid carboxypeptidase was investigated in rat liver, normal human skin (CRL 1501) and lung (WI-38) fibroblasts, galactosialidosis skin fibroblasts (GM 00806) and transformed lung fibroblasts (WI-38 VA 13). Results of differential and isopycnic centrifugations and osmotic activation experiments clearly indicate that the enzyme is located in lysosomes, in agreement with observations suggesting that carboxypeptidase is the protective protein of the 'Galjaard complex' which is defective in galactosialidosis.     

Subcellular localization of ribonucleotide reductase in Novikoff hepatoma and regenerating rat liver

The subcellular localization of ribonucleotide reductase was ascertained in Novikoff heptoma and normal and regenerating rat tissue. Over 90% of the cellular ribonucleotide reductase is found to be associated with a membrane fraction derived from the postmicrosomal supernatant after centrifugation at 78,000g for 18 hr which bands at 1.3 m sucrose in a discontinuous sucrose gradient. The properties of this particular ribonucleotide reductase are similar to those reported for mammalian ribonucleotide reductase. This membrane fraction, which contains ribonucleotide reductase, had been previously shown to contain a DNA polymerase whose activity is related to cell proliferation. The association of these two enzymes involved in DNA synthesis leads to the suggestion that there may exist a complex of enzymes involved in deoxynucleotide and DNA synthesis in this membrane fraction.     

Subcellular localization and substrate specificity of dolichol kinase from rat liver

When purified subcellular fractions were prepared from rat liver and assayed for dolichol kinase activity using pig liver dolichol as a substrate, the microsomes were found to contain the highest specific activity and greater than 75% of the total actvity. With regard to substrate specificity, the microsomal enzyme showed a marked preference for saturation of the α-isoprene: dolichol-16 and -19 were 2.5-fold more active than the corresponding polyprenols. For a given class of prenol, the 16 and 19 isoprenologs exhibited similar activity, whereas the 11 isoprenolog appeared less active. The enzyme was twice as active against the naturally occurring polyprenol-16 (α-cis-isoprene) compared to synthetic α-trans-polyprenol-16. Taken together, the data indicate that the α-isoprene specificity follows the order: saturated>cis>trans. In addition, all-trans-2,3-dihydrosolanesol was not a substrate, suggesting that at least one cis isoprene residue is required.