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  • 1
    Electronic Resource
    Electronic Resource
    Glyoxysomal and mitochondrial malate dehydrogenase of watermelon (Citrullus vulgaris) cotyledons (1977)
    Springer
    Planta 136 (1977), S. 211-220 
    Details
    ISSN: 1432-2048
    Keywords: Citrullus ; Isoenzymes ; Malate dehydrogenase ; Enzyme subunits ; Mitochondria ; Glyoxysomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Molecular properties of the glyoxysomal and mitochondrial isoenzyme of malate dehydrogenase (EC 1.1.1.37; L-malate: NAD+ oxidoreductase) from watermelon cotyledons (Citrullus vulgaris Schrad.) were investigated, using completely purified enzyme preparations. The apparent molecular weights of the glyoxysomal and mitochondrial isoenzymes were found to be 67,000 and 74,000 respectively. Aggregation at high enzyme concentrations was observed with the glyoxysomal but not with the mitochondrial isoenzyme. Using sodium dodecyl sulfate electrophoresis each isoenzyme was found to be composed of two polypeptide chains of identical size (33,500 and 37,000, respectively). The isoenzymes differed in their isoelectric points (gMDH: 8,92, mMDH: 5.39), rate of heat inactivation (gMDH: τ1/2 at 40°C=3.0 min; mMDH: stable at 40°C; τ1/2 at 60°C=4.5 min), adsorption to dextran gels at low ionic strenght, stability against alkaline conditions and their pH optima for oxaloacetate reduction (gMDH: pH 6.6, mMDH: pH 7.5). Very similar pH optima, however, were observed for L-malate oxidation (pH 9.3–9.5). The results indicate that the glyoxysomal and mitochondrial MDH of watermelon cotyledons are distinct proteins of different structural composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385987
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  • 2
    Electronic Resource
    Electronic Resource
    Glyoxysomal and mitochondrial malate dehydrogenase of watermelon (Citrullus vulgaris) cotyledons (1977)
    Springer
    Planta 136 (1977), S. 221-228 
    Details
    ISSN: 1432-2048
    Keywords: Citrullus ; Isoenzymes ; Kinetics ; Malate dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Kinetic parameters of the glyoxysomal and mitochondrial malate dehydrogenase (EC 1.1.1.37) of watermelon (Citrullus vulgaris Schrad.) cotyledons were compared. The data were obtained by initial rate experiments at pH 8.5 in both directions of the reaction using homogeneous enzyme preparations. Substrate inhibition at physiologically significant concentrations was observed with reduced nicotinamide adenine dinucleotide (NADH) (50% inhibition at 0.65 mmol·l-1 NADH), but not with oxaloacetate, L-malate or oxidized nicotinamide adenine dinucleotide. The inhibition of both isoenzymes by 5′adenosine monophosphate was studied. Inhibition was found to be competitive with respect to NADH and non-competitive with respect to oxaloacetate. The apparent inhibitor constants at 200 μmol·l-1 of the fixed substrates were 3.2 and 1.6 mmol·1-1 for NADH, and 3.2 and 5.2 mmol·l-1 for oxaloacetate with the glyoxysomal and mitochondrial isoenzymes, respectively. The energy of activation was determined for oxaloacetate reduction by glyoxysomal (E a =3.14×104J×mol-1) and mitochondrial (E a =4.10×104 J x mol-1) MDH from Arrhenius plots, which exhibited constant slopes throughout the range of thermal stability. Despite considerable structural differences, the results indicate very similar kinetic behaviour of the glyoxysomal and mitochondrial isoenzymes. The physiological significance of the data are discussed in relation to the gluconeogenic processes occuring in cotyledons during germination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385988
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Import of glyoxysomal malate dehydrogenase precursor into glyoxysomes: A heterologous in-vitro system (1986)
    Springer
    Planta 167 (1986), S. 87-93 
    Details
    ISSN: 1432-2048
    Keywords: Citrullus ; Enzyme transport (posttranslational) ; Glyoxysome ; Malate dehydrogenase ; Ricinus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A heterologous in-vitro system is described for the import of the precursor to glyoxysomal malate dehydrogenase from watermelon (Citrullus vulgaris Schrad., cv. Kleckey's Sweet No. 6) cotyledons into glyoxysomes from castor-bean (Ricinus communis L.) endosperm. The 41-kDa precursor is posttranslationally sequestered and correctly processed to the mature 33-kDa subunit by a crude glyoxysomal fraction or by glyoxysomes purified on a sucrose gradient. The import and the cleavage of the extrasequence is not inhibited by metal chelators such as 1,10-phenanthroline and ethylenediaminetetraacetic acid. Uncouplers (carbonylcyanide m-chlorophenylhydrazone), ionophores (valinomycin), or inhibitors of oxidative phosphorylation (oligomycin) and ATP-ADP translocation (carboxyatractyloside) do not interfere, thus indicating the independence of the process of import by the organelle from the energization of the glyoxysomal membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00446373
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Glyoxysomal malate dehydrogenase of watermelon cotyledons: De novo synthesis on cytoplasmic ribosomes (1977)
    Springer
    Planta 134 (1977), S. 277-285 
    Details
    ISSN: 1432-2048
    Keywords: Citrullus ; Enzyme synthesis ; Glyoxysomes ; Malate dehydrogenase ; Seed germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The development of glyoxysomal malate dehydrogenase (gMDH, EC 1.1.1.37) during early germination of watermelon seedlings (Citrullus vulgaris Schrad.) was determined in the cotyledons by means of radial immunodiffusion. The active isoenzyme was found to be absent in dry seeds. By density labelling with deuterium oxide and incorporation of [14C] amino acids it was shown that the marked increase of gMDH activity in the cotyledons during the first 4 days of germination was due to de novo synthesis of the isoenzyme. The effects of protein synthesis inhibitors (cycloheximide and chloramphenicol) on the synthesis of gMDH indicated that the glyoxysomal isoenzyme was synthesized on cytoplasmic ribosomes. Possible mechanisms by which the glyoxysomal malate dehydrogenase isoenzyme reaches its final location in the cell are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384194
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    Paper (German National Licenses)
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