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Biomedical subjects

Y Natori

Publications and source records attributed to Y Natori.

At least 145 records · Page 8Linked to original sources
PubMed1984

Isolation of two kinds of E. coli K-12 mutants for lysophospholipase L2: one with an elevated level of the enzyme and the other defective in it.

Two kinds of E. coli K-12 mutants for lysophospholipase L2 (located in the inner membrane) were isolated, using an improved version of the colony autoradiographic method developed by Raetz; these were, 1) strains carrying an elevated level of the enzyme and 2) strains defective or temperature-sensitive in the enzyme. Characterization of the crude lysates of these mutants revealed that the differences of lysophospholipase L2 activity are not due to the presence or absence of regulatory factors. Evidence was obtained, by using these mutants, that this lysophospholipase L2 transfers the acyl group of 2-acyl lysophospholipid to phosphatidylglycerol, forming acyl phosphatidylglycerol.

Autoradiography↗
PubMed1984

Heterogeneity of free valine pools for protein synthesis on free and membrane-bound polysomes in rat liver.

When rat liver was pulse-labeled with [3H]valine in vivo, the nascent peptide on membrane-bound polysomes was found to be more highly labeled than that on free polysomes. Nascent peptides were purified from both classes of polysomes and, after hydrolysis, the amino acids were reacted with 14C-labeled 1-fluoro-2,4-dinitrobenzene. The specific activity of [3H]valine was determined from the [14C]-dinitrophenyl-[3H]valine after purification by two-dimensional thin layer chromatography. With this approach we found that the specific activity of [3H]valine in the nascent peptide of membrane-bound polysomes was more than twice that of free polysomes. Moreover, when rats were pretreated with a lysosomal protease inhibitor, the differences between the specific activities of valine in nascent peptides of the two classes of polysomes tended to decrease. Our results indicate the existence of two distinct pools for valine used for protein synthesis in liver cells; one serves as a precursor for the synthesis of secretory proteins on membrane-bound polysomes and the other as a precursor for the synthesis of intracellular proteins on free polysomes.

Animals↗
PubMed1984

Nephritogenic glycoprotein X. Correlation between the purity of nephritogenic glycopeptide, nephritogenoside, and morphological manifestation of glomerulonephritis.

When triglycosyl glycopeptide ( nephritogenoside ) was contaminated with glucosyl, galactosyl, mannosyl, and heteropolysaccharide glycopeptide, a mixed lesion of proliferative glomerulonephritis ( PGN ) with immunofluorescent mesangial pattern and membranous glomerulonephritis (MG) with immunofluorescent granular pattern resulted. It was concluded that PGN was caused by the presence of nephritogenoside and MG by the presence of the heteropolysaccharide glycopeptide in the crude nephritogenic glycopeptide mixtures derived from various solubilization steps used to treat the kidney extracts. Trichloroacetic acid treatment of crude nephritogenic glycopeptide mixtures precipitated the heteropolysaccharide glycopeptide of the MG-inducing factor, thus permitting the separation of nephritogenoside from the heteropolysaccharide glycopeptide by a rather simple technique. Both the heteropolysaccharide glycopeptide and Heymann's antigen (so-called tubular antigen) have a common antigenic substance, but we cannot conclude, at the present state, that both substances are chemically the same. The degree of contamination of pure nephritogenoside by this substance that is antigenically the same as Heymann's antigen (in pure nephritogenoside ) can be chemically and accurately determined, based on the evidence that pure nephritogenoside is a glycopeptide having only three glucose residues as the sugar moiety, that is, by estimating the amount of contaminated monosaccharide components such as galactose, mannose, and N-acetylglucosamine.

Animals↗
PubMed1983

Partial purification and properties of phospholipase A2 from rat liver mitochondria.

Phospholipase A2 of rat liver mitochondria was purified approximately 1,400-fold by extraction with KCl, and chromatographies on a Sephadex G-75 column and a diacyl-glycerophosphocholine-Sepharose affinity column. The purified enzyme was very labile when incubated either at 37 degrees C or 0 degrees C, and lost its activity within a few hours. Phospholipids or detergents in the solution protected the enzyme against inactivation. The purified phospholipase A2 preferentially hydrolyzed phosphatidylethanolamine, especially if it contained linoleic acid. The enzyme showed low activity for phosphatidylcholine or phosphatidylinositol.

Animals↗
PubMed1983

Influence of chronic renal failure on protein synthesis in rat liver and muscle.

Protein-synthetic activity in the liver and muscle of rats with chronic renal failure (CRF) of 2 weeks' duration was studied by examining RNA/DNA ratios and polysome profiles and in vitro protein synthetic activity of isolated polysomes. CRF was found to cause differential effects on protein synthesis in the liver and muscle. In the liver, CRF caused impairment of protein synthesis only in the fed condition; CRF rats maintained the same "basal" protein synthetic activity as the sham-operated control rats upon 18 hours' starvation. In the muscle, the effect of CRF was manifested only in the starved condition; CRF caused extensive disaggregation of polysomes when animals were starved. It is proposed that the muscle serves as a "reserve" protein when animals sustain a protein-catabolic state such as CRF.

Animals↗
PubMed1983

Enzyme linked immunosorbent assay for Heymann's antigen as a contaminating minor component in nephritogenic glycopeptide, nephritogenoside.

An enzyme linked immunosorbent assay (ELISA) was introduced for the detection of nephritogenic glycopeptide, nephritogenoside and Heymann's antigen. In the fraction of crude nephritogenoside which induced membranous glomerulonephritis (besides proliferative glomerulonephritis) in rats, both nephritogenoside and Heymann's antigen were detected by ELISA. On the other hand, in the sample of pure nephritogenoside which induced only proliferative glomerulonephritis, Heymann's antigen was not detected at all. These results indicate that crude nephritogenoside preparation contains Heymann's antigen as an inducing factor of membranous glomerulonephritis in homologous animals. In addition to TCA treatment or DEAE-cellulose column chromatography, gel filtration on Bio-Gel P200 was a good tool for the removal of Heymann's antigen from nephritogenoside.

Animals↗
PubMed1982

The role of translational inhibitor in ethionine-induced inhibition of protein synthesis.

The soluble fraction from rat liver contains an inhibitor of protein chain initiation when tested in a cell-free protein-synthesizing system derived from rabbit reticulocytes. The administration of ethionine to rats increased the inhibitory activity in the liver. This liver inhibitor displayed properties similar to those of hemin-controlled inhibitor found in rabbit reticulocytes: (i) the liver inhibitor inhibited protein chain initiation in rabbit reticulocyte lysate with characteristic biphasic kinetics; (ii) the liver inhibitor disaggregated the reticulocyte polysomes with a concomitant increase in 80 S ribosomes; (iii) the inhibition was prevented or reversed by eIF-2. The activation of the liver inhibitor by ethionine was rapidly and completely counteracted by the subsequent administration of methionine and adenine to rats. The mechanism of inhibition of protein synthesis by ethionine was discussed in the light of these findings.

Animals↗
PubMed1982

A cell-free system from ethionine-treated rat liver active in initiation of protein synthesis.

A cell-free protein-synthesizing system active in initiation of translation of both endogenous mRNA and exogenous mRNA has been obtained from postmitochondrial supernatant (S-12) of the liver of ethionine-treated rats by adding reticulocyte ribosomal extract as a source of initiation factor. Formation of polysomes in the course of protein synthesis in vitro has also been demonstrated. Homogenization of the liver in the presence of 50 microM hemin stabilizes the initiation activity of S-12 fraction, which otherwise decays rapidly even at 0 degrees C. The mechanism of inhibition of protein synthesis by ethionine is discussed in view of these results.

Animals↗
PubMed1981

Cell-free synthesis of ornithine aminotransferase of rat liver.

Mitochondrial ornithine aminotransferase was synthesized in a rabbit reticulocyte cell-free system using polysomal mRNA from rat liver. Upon analyzing the primary translation product by electrophoresis and fluorography, we found that ornithine aminotransferase is synthesized not as a large precursor but as one with its authentic size. Free ribosomes were found to be the main site of synthesis of ornithine aminotransferase.

Animals↗
PubMed1980

Purification and properties of a membrane-bound phospholipase A2 from rat ascites hepatoma 108A cells.

A phospholipase A2 bound tightly to the particulate fractions of rat ascites hepatoma cells was purified approximately 13,000-fold with a reasonably high yield (34%) by extraction with sodium cholate, ammonium sulfate fractionation, solubilization with sodium dodecyl sulfate, column chromatographies on Sephadex G-150 in the presence of sodium dodecyl sulfate, and on DEAE-cellulose and CM-cellulose in the presence of Triton X-100. The enzyme has a unique substrate specificity; namely, it preferentially hydrolyzes phosphatidylethanolamine and, to a lesser degree, phosphatidylglycerol. However, it does not attack phosphatidylcholine, phosphatidic acid or cardiolipin in the present experimental conditions. The final preparation shows both phospholipase A2 and lysophospholipase L2 activities, but neither lysophospholipase L1 nor lipase activity. The purified enzyme has a rather broad pH optimum ranging from 7 to 9, requires Ca2+, and is resistant to heat-treatment at 95 degree C for 5 min.

Animals↗
PubMed1979

Direct association of messenger RNA-containing ribonucleoprotein particles with membranes of the endoplasmic reticulum in ethionine-treated rat liver.

The administration of ethionine to female rats causes breakdown of hepatic polysomes. The fate of the mRNA molecules after polysome breakdown was investigated by measuring the amount of poly(A)-containing mRNA in membranous and non-membranous fractions obtained from the cytoplasm of ethionine-treated rat liver. The amount of poly(A)-containing mRNA in the membrane fraction of ethionine-treated liver was found to be the same as that of normal liver. When poly(A)-containing mRNAs from various fractions were translated in a wheat germ system and the products were isolated by immunoprecipitation, the albumin-specific mRNA was found exclusively in the membrane fraction of both normal and ethionine-treated livers. The membrane-bound mRNA in ethionine-treated liver, selectively labeled with [14C]orotate, was banded in CsCl gradient centrifugation at 1.42 g/ml which corresponds to the previously reported mRNA-containing ribonucleoprotein particles. From these results, we concluded that even after the polysome disaggregation by ethionine, most of the mRNA of membrane-bound polysomes remains attached to the endoplasmic reticulum membranes independently of ribosomes and the nascent polypeptide chains.

Animals↗
PubMed1979

The effect of protein depletion on the rate of protein synthesis in rat liver.

In order to understand the mechanism of decreased protein synthesis in the liver of rats fed a protein-free diet, the average polypeptide chain assembly time (tc) was measured by the method of Mathews et al. (J. Biol. Chem. (1973) 248, 1329). For rats fed a normal diet, tc in liver in vivo was 1.28 min. A 10-day period of protein depletion led to a value of tc = 2.08 min, corresponding to a 38% depression in polypeptide elongation rate. Protein depletion caused an extensive breakdown of hepatic polysomes and refeeding of a complete mixture of amino acids resulted in rapid recovery of polysomal profile. But tc in the liver of the refed animals gave still depressed value of 1.95 min. The amount and size distribution of poly(A)-containing mRNA in the liver, as determined by [3H]poly(U) hybridization, were the same for normal and depleted groups. These results suggest that both initiation and elongation steps of protein synthesis are depressed in the liver of protein-depleted rats. Refeeding of amino acid mixture rapidly restores initiation but not elongation activity.

Animals↗