Nov 15, 1975

On the mechanism of ketogenesis and its control. Purification, kinetic mechanism and regulation of different forms of mitochondrial acetoacetyl-CoA thiolases from ox liver

European Journal of Biochemistry
W HuthW Seubert

Abstract

1. Two mitochondrial forms of acetoacetyl-CoA thiolases designated as enzyme A and enzyme B were crystallized from ox liver. They could be shown to be homogenous by polyacrylamide gel electrophoresis. 2. In direction of acetoacetyl-CoA cleavage enzyme A shows a double competitive substrate inhibition when acetoacetyl-CoA is varied at different fixed CoA concentrations. With enzyme B a parallel kinetic pattern is obtained when acetoacetyl-CoA is varied at different fixed CoA concentrations. In direction of acetoacetyl-CoA synthesis both enzymes show linear reciprocal plots of initial velocities against acetyl-CoA concentrations in absence of CoA. These initial velocity kinetics in the forward and in the reverse direction are in accordance with a ping-pong mechanism of reaction for both enzymes involving an acetyl-S-enzyme as intermediate. 3. Under saturating concentrations of substrate, the ratios of acetoacetyl-CoA synthesis/aceto-acetyl-CoA cleavage is 0.31 for enzyme A and 0.08 for enzyme B. The maximum velocity in direction of acetoacetyl-CoA synthesis of enzymes A and B are 0.43 mumol X min-1 X unit thiolase-1 and 0.10 mumol X min-1 X unit thiolase-1, respectively. 4. Both enzymes show nearly the same affinity for acetyl-Co...Continue Reading

  • References16
  • Citations13

References

  • References16
  • Citations13

Citations

Mentioned in this Paper

Fluctuation
Exertion
Enzymes, antithrombotic
Coenzyme A
Ketogenesis
Protoplasm
Acetyl Coenzyme A
Cytokinesis of the Fertilized Ovum
Mitochondria, Liver
NADH

About this Paper

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