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Biochemistry

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Moderate

Phosphocreatine Acts as an ATP Buffer

BIOCHM-JNVL9N

Creatine kinase catalyzes the reversible phosphorylation of creatine by ATP as follows:

$${ \text{ATP +} }{\space \text{creatine} \rightleftharpoons \text{ phosphocreatine + ADP } }$$

Phosphocreatine acts as an ATP “buffer.” It both stores excess ATP and rapidly delivers ATP when needed, especially in muscle and brain tissue. Under typical intracellular concentrations of the reactants and products, the reaction operates at near equilibrium (${ \Delta G\sim 0 }$).

Considering the above information and the table of standard​ phosphoryl-group transfer potentials (below), which of the following statements correctly describes how this reaction operates under the given conditions?

Molecule Abbrev. ${ \Delta G }^{ °\prime }$ ( ${ kJ mol }^{ -1 }$)
Phosphoenolpyruvate PEP -61.9
1,3-Bisphosphoglycerate BPG -49.4
Phosphocreatine PC -43.1
Adenosine Triphosphate ATP -30.5
Glucose-1-Phosphate G1P -20.9
Glucose-6-Phosphate G6P -13.8
Glycerol-3-Phosphate Gy3P -9.2
A

Under standard conditions, the phosphorylation of creatine is an exergonic reaction.

B

Under high energy demand, the reaction catalyzed by creatine kinase will generate ATP in an exergonic reaction.

C

Under resting conditions, when the demand for ATP is low, creatine will accumulate as a ready source of energy.

D

The phosphorylation of creatine by ATP to phosphocreatine represents a wasteful loss of energy contained in the high-energy​ molecule ATP.

E

Under high energy demand, the reaction catalyzed by creatine kinase will generate phosphocreatine in an endergonic reaction.