The specific activity of D-3-hydroxybutyrate dehydrogenase is reduced by about a third in liver and heart mitochondria of hyperthyroid rats. State 3 respiration is also reduced in isolated mitochondriafrom the same animals when DL-3-hydroxybutyrateis the substrate. Determination of the kinetic parameters of the membrane-bound D-3- hydroxybutyratedehydrogenase in liver of hyperthyroidrats reveals a decreased in maximal velocity (V,,,). The Michaelis and dissociation constants of NAD+ and D-3- hydroxybutyrate are also significantly influenced, thus indicating that both the affinity and the binding of this enzyme toward its substrates are affected. In hyperthyroidrats a significant ketone-body increase is found in both liver and heart: in blood, an almost doubled concentration can be measured. At the same time, in heart mitochondria of these animals the activity of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase is significantly reduced. The decrease in both D-3-hydroxybutyrate dehydrogenase and 3-oxoacid coenzyme A-transferase associated with the increase in ketone bodies sup- ports the suggestion that there is a lower utilizationof these compounds by peripheral tissues. In the blood of hyperthyroidrats a higher D-3-hydroxybutyrate/acteoacetate ratio is also found, probably resulting from a selective utilization of the two compounds in this pathological state.
Ketone-Body Metabolism in Hyperthyroid Rats: Reduced Activity of D-3- HydroxybutyrateDehydrogenasein Both Liver and Heart and of Succinyl- CoenzymeA: 3-OxoacidCoenzymeA-Transferasein Heart
ROSA LIPPOLIS;NICOLA ALTAMURA;
1988
Abstract
The specific activity of D-3-hydroxybutyrate dehydrogenase is reduced by about a third in liver and heart mitochondria of hyperthyroid rats. State 3 respiration is also reduced in isolated mitochondriafrom the same animals when DL-3-hydroxybutyrateis the substrate. Determination of the kinetic parameters of the membrane-bound D-3- hydroxybutyratedehydrogenase in liver of hyperthyroidrats reveals a decreased in maximal velocity (V,,,). The Michaelis and dissociation constants of NAD+ and D-3- hydroxybutyrate are also significantly influenced, thus indicating that both the affinity and the binding of this enzyme toward its substrates are affected. In hyperthyroidrats a significant ketone-body increase is found in both liver and heart: in blood, an almost doubled concentration can be measured. At the same time, in heart mitochondria of these animals the activity of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase is significantly reduced. The decrease in both D-3-hydroxybutyrate dehydrogenase and 3-oxoacid coenzyme A-transferase associated with the increase in ketone bodies sup- ports the suggestion that there is a lower utilizationof these compounds by peripheral tissues. In the blood of hyperthyroidrats a higher D-3-hydroxybutyrate/acteoacetate ratio is also found, probably resulting from a selective utilization of the two compounds in this pathological state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
