Acyl CoA synthetase, is an enzyme that requires ATP to function. However, the re

Question

Acyl CoA synthetase, is an enzyme that requires ATP to function. However, the reaction that charges CoA with the acyl group is freely reversible with an equilibrium constant of 1. Why is charging the CoA freely reversible with splitting the acyl from the CoA molecule?

A. the phosphate group on the CoA can provide energy for hydrolysis

B. the enzyme actually favors the reverse reaction (positive deltaG)

C. the reaction is not reversible

D. the thioester bond on Acyl CoA provides energy for the reverse reaction

E. there is a second enzyme that uses ATP to un-charge the acyl CoA

Explanation / Answer

Here the option A is correct. The Acyl CoA synthetase catalyzes the conversion of acetate, ATP and coenzyme A into acetyl-CoA and AMP. The acetyl-CoA synthetase is regulated by reversible acetylation via the competing activities of a protein acetyltransferase and a protein deacetylase. Acetyl-CoA synthase is enzymatically inactive when acetylated and activated by deacetylation. Hence The enzyme involved in both reaction i.e. forward and backward, is same but the regulation of enzyme is different. The thioester bond cannot provide energy as the dissociation of bond consumes energy not release the energy. Also the enzyme cannot favour the reverse reaction as equilibrium constant is 1. Hence the option A is correct.

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