Comparative analysis of the reduction of oxaloacetate by human hepatoma and normal liver extracts.
An apparent activation of the malate dehydrogenase activity is observed in the double-reciprocal plot at high oxaloacetate concentrations when human hepatoma extracts are analyzed. This phenomenon does not occur in healthy liver samples. In hepatoma extracts, the ratio of lactate dehydrogenase to malate dehydrogenase activities becomes five-fold higher than that of normal liver. Experiments performed with mixtures of both purified enzymes and, conversely, by using oxamate, a specific inhibitor of lactate dehydrogenase, reveal that the deviation in Michaelis-Menten behavior observed is due to the oxaloacetate reductase activity of lactate dehydrogenase instead of the presence of a novel malate dehydrogenase isoenzyme.
Mazo
A
A
Departament de Bioquímica i Fisiologia, Facultat de Química, Universitat de Barcelona, Spain.
Forner
A
A
Domènech
C
C
Busquets
M
M
Gelpí
J L
JL
Cortés
A
A
D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008113:Liver Neoplasms / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000378:metabolism; D010071:Oxaloacetates / Q000378:metabolism*; D010084:Oxidation-Reduction
D007527:Isoenzymes; D010071:Oxaloacetates; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase