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Biomedical subjects

T Zimmermann

Publications and source records attributed to T Zimmermann.

At least 199 records · Page 11Linked to original sources
PubMed1983

Qualitative and quantitative changes in hepatic lipoprotein particles following acute injury of the rat liver induced by thioacetamide.

Acute intoxication of the rat liver with a single dose of 100 mg thioacetamide (TAA)/kg body weight causes within 48 h a fatty liver and a heterogeneous reaction in the hepatocytes. This affects principally the centrilobular liver parenchymal cells (zone 3) and to a lesser extent the periportal ones (zone 1). Ultrastructural analysis was performed to determine to what extent the formation of lipid-carrying particles of the very low density type (VLDL) is changed in affected hepatocytes in zones 1 and 3. Being morphologically the most conspicuous site of VLDL processing, the Golgi complex was chosen for quantitation by measuring its volume, VLDL content and particle size. The concentration and composition of the liver lipids were determined, biochemically. After TAA treatment of the liver the number of Golgi-VLDL particles is significantly reduced to about 50% in both the lobular zones examined. In addition, distinct classes of size-modified Golgi-VLDL particles appear which show an abnormally wide size distribution pattern. In periportal hepatocytes the size distribution of Golgi-VLDL particles shows a clear shift towards smaller particles homogeneous in size (mean diameter 39 nm). In contrast, centrilobular hepatocytes contain particles of very heterogeneous size, the mean diameter of which is nearly doubled (77 nm). The decrease in VLDL particle number and their size modification induced by TAA is not accompanied by significant changes in the volume of the Golgi complex. Biochemical analysis showed that the accumulation of lipids in the TAA-treated liver, mainly evident morphologically as drop-like deposits in the central area of the liver lobules, is due to an increase in triglycerides (TG) by 23 mumol/g liver wet weight, which represents nearly 95% of the accumulated lipids. Despite the striking elevation of the absolute cholesterol ester (CHOL-E) content (2 mumol/g liver wet weight), this corresponds to only 5% of the newly accumulated lipids. Our electron optical and biochemical results support the suggestion that, in spite of the markedly different intralobular reaction of TAA-intoxicated hepatocytes, the formation of triglyceride-carrying particles is altered significantly in both lobular zones examined.

Acetamides↗
PubMed1983

Maternal-fetal transfer of free fatty acids during late gestation in the rat.

The maternal-fetal transfer of free fatty acids during late gestation in the rat has been investigated. The isotopic tracer technique and a mathematical model were used. From the results the conclusion can be drawn that the fetus from day 15 to 19 of pregnancy derives only 10% of the fetal fatty acids from the maternal circulation.

Animals↗
PubMed1982

Purification of L-glutamate-dependent citrate lyase from Clostridium sphenoides and electron microscopic analysis of citrate lyase isolated from Rhodopseudomonas gelatinosa, Streptococcus diacetilactis and C. sphenoides.

Citrate lyase from Clostridium sphenoides was purified 72-fold with a yield of 11%. In contrast to citrate lyase from other sources the activity of this enzyme was strictly dependent on the presence of L-glutamate. The purified enzyme was only stable in the presence of 150 mM L-glutamate or 7 mM L-glutamate plus glycerol, sucrose or bovine serum albumin. Changes of the L-glutamate pool and of enzyme activity in growing cells of C. sphenoides indicated that citrate lyase activity in this organism was regulated by the intracellular L-glutamate concentration. Citrate lyase isolated from C. sphenoides, Rhodopseudomonas gelatinosa and Streptococcus diacetilactis was investigated by electron microscopy using the negative staining technique. Three different projections of enzyme molecules were observed: 'star' form, 'ring' form and 'triangle' form. In samples from R. gelatinosa and S. diacetilactis, star and ring forms occurred in a ratio of about 1:9. Using the enzyme from S. diacetilactis it was demonstrated that this ratio could be altered in favour of the star form by the addition of citrate or tricarballylate. The triangle form was observed in less than 1% of all evaluated molecules and may represent a transition form. In lyase samples from C. sphenoides there existed a correlation between enzyme activity and the proportion of stars and rings at varying concentrations of L-glutamate.

Bacteria↗
PubMed1982

Analysis of structure-function relationships in citrate lyase isolated from Rhodopseudomonas gelatinosa as revealed by cross-linking and immunoelectron microscopy.

Citrate lyase (EC 4.1.3.6) isolated from Rhodopseudomonas gelatinosa was analyzed using cross-linking experiments and immunoelectron microscopy. Different cross-linking reagents and antibodies directed against citrate lyase and specifically against all three subunit types (L, M and S) were applied. A structure-function model is proposed for citrate lyase from R. gelatinosa: the enzyme occurs in two configurations, 'rings' and 'stars'. The ring contains two identical layers each consisting of three subunits L, with one subunit S as a polar cap sitting on each L, and three subunits M in alternating sequence (18 subunits altogether). In the star, the same 18 subunits are arranged in a different way. Whereas the subunits L are located at the periphery, the subunits M are concentrated in the center of the particle. The subunits S are positioned relative to L as in the ring; however, their location relative to the subunits M is changed. By transition from ring to star, areas on S are brought into contact with areas on M by rotation of structural units, consisting of one L, one M and one S subunit per layer, against each other, with S of one structural unit close to M of the neighbouring structural unit. This transition is assumed to work also in reversed direction. The observation of rings and stars as two distinct molecular forms is proposed to reflect the two states of citrate lyase, the ring being the form where substrate is bound by acyl exchange, and the star being the form where the substrate is consumed by cleavage, i.e. the catalyzed reaction is completed.

Cross-Linking Reagents↗
PubMed1982

Properties of purified Orange II azoreductase, the enzyme initiating azo dye degradation by Pseudomonas KF46.

Orange II azoreductase [NAD(P)H: 1-(4'-sulfophenylazo)-2-naphthol oxidoreductase], an enzyme catalyzing the reductive cleavage of the azo bridge of Orange II and related dyes, was purified to electrophoretic homogeneity from Pseudomonas species, strain KF46. This organism utilized carboxy-Orange II [1-(4'-carboxyphenylazo)-2-naphthol] but not Orange II as the sole source of carbon, energy, and nitrogen. Orange II azoreductase was induced 80-fold by both Orange II and carboxy-Orange II. With two successive runs of affinity chromatography using two chromatographic media with different triazinyl dyes as ligands, the enzyme was purified 120-fold with 43% yield. The purified enzyme is a monomer with a molecular weight of 30,000. Its Km values were 1.5 microM for both Orange II and carboxy-Orange II, 5 microM for NADPH, and 180 microM for NADH. A survey of the efficiency of various Orange dyes as substrates for Orange II azoreductase showed that: (a) a hydroxy group in the 2-position of the naphthol ring is required; (b) charged groups in proximity to the azo group hinder the reaction; (c) a second polar substituent on the dye molecule impedes the reaction; (d) electron-withdrawing groups on the phenyl ring accelerate the reaction.

Azo Compounds↗
PubMed1982

Studies on the hypertriglyceridemia in pregnant rats.

The study has been performed in order to obtain information on the mechanism responsible for the hypertriglyceridemia found in pregnant rats. The results show that the whole plasma triglyceride flux is increased by 65% in late gestation. It has been found that labeled VLDL triglyceride originating from pregnant rats shows no delay in plasma disappearance when injected into the circulation of non pregnant female rats. Contrariwise, labeled VLDL triglyceride originating from non pregnant rats when injected into pregnant rats shows a delay in disappearance from the circulation. From these results the conclusion can be drawn that the delay in labeled plasma triglyceride disappearance in late gestation is not caused by a possibly abnormal VLDL showing a decrease in affinity of lipoprotein substrate for lipoprotein lipase. Therefore, we interpret the delay in labeled plasma triglyceride disappearance in late gestation in terms of a lowered removal capacity of plasma triglyceride by extrahepatic tissue.

Animals↗
PubMed1981

Substrate specificity of citrate lyase deacetylase of Rhodopseudomonas gelatinosa and Rhodopseudomonas palustris.

Citrate lyase (EC 4.1.3.6) isolated from Rhodopseudomonas palustris was investigated with regard to its kinetic properties and its subunit composition. This enzyme was inactivated by citrate lyase deacetylase (EC 3.1.2.-) of Rhodopseudomonas gelatinosa. A corresponding cross-reaction was measured with partially purified deacetylase of R. palustris and citrate lyase of R. gelatinosa. The three different subunit types (alpha, beta, and gamma) of citrate lyase from R. gelatinosa wee purified to homogeneity, and antibodies were prepared against each of the three subunits and against the native enzyme complex. In corresondence with the enzymatic interactions, immunological cross-reactions were found between anti-enzyme and anti-large subunit antibodies and citrate lyase from R. palustris. On the other hand, no immunological cross-reactions were detectable among each of the antibodies and citrate lyases from Enterobacter aerogenes, Streptococcus diacetilactis, and Clostridium sphenoides. Antibodies against the large subunit of citrate lyase inhibited the deacetylase, but antibodies against the middle and small subunits did not, indicating that the large subunits of citrate lyase are involved in binding the deacetylase.

Antibodies, Bacterial↗
PubMed1980

Studies on the disappearance of palmitate-1-14C from the plasma of pregnant rats.

Intravenously injected radioactive fatty acids disappear from the circulation at an ever-decreasing rate; about 1% of the injected label remains in plasma for hours. This slow elimination of label can be explained by an extensive recycling of label or by a slows turnover of a portion of the injected label. The results show that a recycling of label can not be responsible for the slow elimination of label, because 1. the specific activities of the tissue fatty acids were much lower than the specific activity of the plasma free fatty acids, and 2. reinjection of the remaining label of 1% into control animals showed the same slow elimination of label. An interpretation of the experiments could be that some fatty acids (about 1%) have a dissociation rate from albumin that is much lower than others, and thus they might be responsible for the late portion of the disappearance curve.

Adipose Tissue↗
PubMed1979

Synthesis of arachidonic acid in the human placenta in vitro.

The syntheses of arachidonic acid and total fatty acids were measured in human placentas at the end of the first trimester and at term using 14C-acetate in in vitro incorporation experiments. The rates of arachidonic acid synthesis were determined to be 0.70 (first trimester) and 0.64 (term) mumol/h/100 g of placental tissue. The calculated rates of total fatty acid synthesis amount to 0.5 (first trimester) and 0.6 (term) mumol palmitate-equivalents/h/100 g. The results suggest that the human placenta seems to be not dependent on maternal arachidonic acid. Near term the placenta even could be source of arachidonic acid.

Arachidonic Acids↗
PubMed1979

Oxidation and synthesis of fatty acids in human and rat placental and fetal tissues.

The rat fetus (day 21 of pregnancy) covers its fatty acid (FA) demands at equal amounts both by maternal-fetal FA transfer and fetal FA synthesis. At the end of the first trimester the human fetal FA synthesis is too small to cover the fetal FA requirements. Therefore, the transfer of FA from the mother to the fetus seems to be the predominant source of fetal FA. The FA oxidation is greater than the FA synthesis in human and rat placenta as well as in the human fetus at the end of the first trimester, whereas the rat fetus (day 21 of pregnancy) oxidizes and synthesizes FA at equal amounts.

Animals↗