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Regulation of ketogenesis mitochondrial acetyl coenzyme a acetyl transferase ec 2.3.1.9 from rat liver initial rate kinetics in the presence of the product coenzyme a reveal intermediary plateau regions






European Journal of Biochemistry 128(2-3): 413-420

Regulation of ketogenesis mitochondrial acetyl coenzyme a acetyl transferase ec 2.3.1.9 from rat liver initial rate kinetics in the presence of the product coenzyme a reveal intermediary plateau regions

The analysis of the initial-rate kinetics of the liver mitochondrial acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase) in the direction of acetoacetyl-CoA synthesis under product inhibition was performed. Acetyl-CoA acetyltransferase shows a hyperbolic response of reaction velocity to changes in acetyl-CoA concentrations with an apparent Km of 0.237 .+-. 0.001 mM. CoASH is a (non-competitive) product inhibitor with a Kis of 22.6 .mu.M and shifts the apparent Km for acetylCoA to the physiological concentration of this substrate in mitochondria (S0.5 = 1.12 mM in the presence of 121 .mu.M CoASH). CoASH causes a transformation in the Michaelis-Menten kinetics into initial-rate kinetics with 4 intermediary plateau regions. The product analog desulfo-CoA triggers a negative cooperativity as to the dependence of the reaction velocity on the acetyl-CoA concentration. These product effects drastically desensitize the acetyl-CoA acetyltransferase in its reaction velocity response to the acetyl-CoA concentrations and simultaneously extend the substrate dependence range. Thus a control of acetoacetyl-CoA synthesis by the substrate is established over the physiological acetyl-CoA concentration range. This control mechanism may be the key in establishing the rates of ketogenesis.


Accession: 006288907



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