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  • Citrate synthase  (2)
  • Congenital cataract  (2)
  • OCT1  (2)
  • 1995-1999  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Transport of small organic cations in the rat liver (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 354 (1996), S. 320-326 
    Details
    ISSN: 1432-1912
    Keywords: Rat liver ; Transport of organic cations ; OCT1 ; Type I hepatic transport of cationic drugs ; 1-Methyl-4-phenylpyridinium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The kidneys and the liver are the principal organs for the inactivation of circulating organic cations. Recently, an organic cation transporter (OCT1) has been cloned from rat kidney. In order to answer the question whether OCT1 is involved also in hepatic uptake of organic cations, the pharmacological characteristics of organic cation transport in hepatocytes were compared to the characteristics of transiently expressed OCT1. Primary cultures of rat hepatocytes avidly accumulated the small organic cation 3H-1-methyl-4-phenylpyridinium (3H-MPP+). At equilibrium, the hepatocytes accumulated 3H-MPP+ 56-fold. Initial rates of specific 3H-MPP+ transport in hepatocytes were saturable. The half-saturating concentration was 13 μmol/l. 3H-MPP+ transport was sensitive to quinine (Ki = 0.79 μmol/l) and cyanine863 (Ki = 0.097 µmol/l). Quinine and cyanine863 are known inhibitors of type I hepatic transport of cationic drugs and of renal excretion of organic cations, respectively. To compare the functional characteristics of 3H-MPP+ transport in hepatocytes with those of OCT1, OCT1 has been heterologously expressed and characterized in a mammalian cell line (293 cells). Initial rates of 3H-MPP+ transport were saturable, the Km being 13 μmol/l. The rank order of inhibitory potencies of various inhibitors was almost identical in hepatocytes and 293 cells transiently transfected with OCT1. There was a positive correlation between the Ki's for the inhibition of 3H-MPP+ transport in isolated hepatocytes and transfected 293 cells (r = 0.85; P〈0.01; n = 8). The results indicate that OCT1 is functionally expressed not only in the kidney but also in hepatocytes where it is responsible for the transport of small organic cations which, in the past, have been classified as type I substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171063
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Transport of small organic cations in the rat liver The role of the organic cation transporter OCT1 (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 354 (1996), S. 320-326 
    Details
    ISSN: 1432-1912
    Keywords: Key words Rat liver ; Transport of organic cations ; OCT1 ; Type I hepatic transport of cationic drugs ; 1-Methyl-4-phenylpyridinium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The kidneys and the liver are the principal organs for the inactivation of circulating organic cations. Recently, an organic cation transporter (OCT1) has been cloned from rat kidney. In order to answer the question whether OCT1 is involved also in hepatic uptake of organic cations, the pharmacological characteristics of organic cation transport in hepatocytes were compared to the characteristics of transiently expressed OCT1. Primary cultures of rat hepatocytes avidly accumulated the small organic cation 3H-1-methyl-4-phenylpyridinium (3H-MPP+). At equilibrium, the hepatocytes accumulated 3H-MPP+ 56-fold. Initial rates of specific 3H-MPP+ transport in hepatocytes were saturable. The half-saturating concentration was 13 μmol/l. 3H-MPP+ transport was sensitive to quinine (Ki = 0.79 μmol/l) and cyanine863 (Ki = 0.097 μmol/l). Quinine and cyanine863 are known inhibitors of type I hepatic transport of cationic drugs and of renal excretion of organic cations, respectively. To compare the functional characteristics of 3H-MPP+ transport in hepatocytes with those of OCT1, OCT1 has been heterologously expressed and characterized in a mammalian cell line (293 cells). Initial rates of 3H-MPP+ transport were saturable, the Km being 13 μmol/l. The rank order of inhibitory potencies of various inhibitors was almost identical in hepatocytes and 293 cells transiently transfected with OCT1. There was a positive correlation between the Ki’s for the inhibition of 3H-MPP+ transport in isolated hepatocytes and transfected 293 cells (r = 0.85; P〈0.01; n = 8). The results indicate that OCT1 is functionally expressed not only in the kidney but also in hepatocytes where it is responsible for the transport of small organic cations which, in the past, have been classified as type I substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171063
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Lens sorbitol dehydrogenase deficiency in a patient with congenital cataract (1995)
    Springer
    European journal of pediatrics 154 (1995), S. 389-391 
    Details
    ISSN: 1432-1076
    Keywords: Sorbitol dehydrogenase ; Lens ; Congenital cataract
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lens sorbitol dehydrogenase activity was assayed in patients with congenital cataracts, senile cataracts, without cataracts and in one fetal lens. In patients with congenital cataracts we did not observe any abnormality of galactose and sorbitol metabolising enzymes in erythrocytes. In one of these patients with inexplicable congenital cataracts lens sorbitol dehydrogenase deficiency was found. Conclusion Determination of galactose metabolising enzymes, sorbitol dehydrogenase and polyols in lenses may help in understanding the mechanism of formation of inexplicable congenital cataracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02072111
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  • 4
    Electronic Resource
    Electronic Resource
    Lens sorbitol dehydrogenase deficiency in a patient with congenital cataract (1995)
    Springer
    European journal of pediatrics 154 (1995), S. 389-391 
    Details
    ISSN: 1432-1076
    Keywords: Key words Sorbitol dehydrogenase ; Lens ; Congenital cataract
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lens sorbitol dehydrogenase activity was assayed in patients with congenital cataracts, senile cataracts, without cataracts and in one fetal lens. In patients with congenital cataracts we did not observe any abnormality of galactose and sorbitol metabolising enzymes in erythrocytes. In one of these patients with inexplicable congenital cataracts lens sorbitol dehydrogenase deficiency was found. Conclusion Determination of galactose metabolising enzymes, sorbitol dehydrogenase and polyols in lenses may help in understanding the mechanism of formation of inexplicable congenital cataracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004310050311
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  • 5
    Electronic Resource
    Electronic Resource
    Ecophysiological studies on citrate-synthase: (I) enzyme regulation of selected crustaceans with regard to temperature adaptation (1995)
    Springer
    Journal of comparative physiology 165 (1995), S. 46-55 
    Details
    ISSN: 1432-136X
    Keywords: Citrate synthase ; Enzyme characteristics ; Temperature adaptation ; Isopod crustacea ; Euphausiid crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The characteristics and properties chromatographically purified citrate synthase from the euphausiids Euphausia superba (Antarctica) and Meganyctiphanes norvegica (Scandinavian Kattegat and Mediterranean Sea) and from the isopods Serolis polita (Antarctica) and Idotea baltica (Baltic Sea) were used to elucidate biochemical mechanisms of temperature adaptation. Additionally, maintenance experiments were carried out on the euphausiids to determine mechanisms of short term acclimation. Temperature optima (between 37 and 45°C) were unrelated to genotypic cold adaptation, but the activation energy of the Antarctic krill E. superba (10.9 kJ · mol-1) was only a quarter of that in other species (41.8–45.1 kJ · mol-1). The minima of apparent Michaelis constants (total range: 4–20 μmol · 1-1 oxaloacetate; 7–45 μmol · 1-1 acetyl-coenzyme A) showed no relation to natural conditions, and no distinct pH optimum occurred at ambient temperatures. In contrast, apparent Michaelis constants and specific enzyme activities were related to maintenance temperatures in M. norvegica, but not in E. superba. The differences between M. norvegica and E. superba can be interpreted as adaptations to the changes in ambient temperature with regard to the respective steno- and eurythermic tolerances of these crustaceans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264685
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  • 6
    Electronic Resource
    Electronic Resource
    Ecophysiological studies on citrate synthase: (II) enzyme regulation of selected crustaceans with regard to life-style and the climatic zone (1995)
    Springer
    Journal of comparative physiology 165 (1995), S. 56-61 
    Details
    ISSN: 1432-136X
    Keywords: Citrate synthase ; Enzyme regulation ; Temperature adaptation ; ATP inhibition ; Crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Citrate synthase is a regulatory enzyme of the energy metabolism pathway controlling the citric acid cycle. It was studied in order to determine modes of enzyme regulation with regard to the life-style of the investigated species. Citrate synthase from crustaceans with different life-styles were compared: the pelagic euphausiids Euphausia superba from the Antarctic and Meganyctiphanes norvegica from the Scandinavian Kattegat and the Mediterranean were compared to the benthic isopods Serolis polita from the Antarctic and Idotea baltica from the Baltic. Citrate synthase was partly purified chromatographically and the influence of adenosine 5′-triphosphate on enzyme activity was examined. Mechanisms of inhibition and inhibitor constants were determined. Two different mechanisms of enzyme regulation by ATP were found. Citrate synthase from isopods was only competitively inhibited, while citrate synthase from euphausiids showed not only competitive inhibition but also activation by low concentrations of ATP. This activation is equivalent to the reversed methanism of uncompetitive inhibition. The ecophysiological relevances of the coupling of these mechanisms are discussed. The degree of competitive inhibition was different in the two groups of investigated crustaceans. Inhibitor constants were similar within the euphausiids but not in isopods, which showed higher or lower inhibition depending on the climatic zone: the colder the ambient temperature the lower the ATP inhibition. A possible mechanism of temperature adaptation through effects of varying inhibition constants is concluded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264686
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