2. The following reaction is catalyzed by the enzyme creatine kinase: Creatine +

Question

2. The following reaction is catalyzed by the enzyme creatine kinase:

Creatine + ATP Creatine phosphate + ADP

Under standard conditions (1 atm, 298 K, pH 7.0, pMg 3.0, and an ionic strength of 0.25 M) with the concentrations of all reactants equal to 10 mM, the Gibbs energy change, G, for this reaction is 13.3 kJ/mol.

a. What is the standard Gibbs energy change, Go, for this reaction?

b. The standard enthalpies of formation for the reactants are as follows: Creatine -540 kJ/mol Creatine Phosphate -1510 kJ/mol ATP -2982 kJ/mol ADP -2000 kJ/mol What is the standard enthalpy change, Ho, for this reaction?

c. What is the standard entropy change, So, for this reaction?

Explanation / Answer

2) a) Given that G = 13.3 kJ/mol

       G = Go + RT InK

   K = [Creatine phosphate] [ ADP] / [Creatine] [ATP] = 10 mM x 10mM/ 10mM x 10mM =1

Hence,

    G = Go + RT In1

         = Go + 0

      G = Go

Therefore,

Go = 13.3 kJ/mol

b) Creatine + ATP Creatine phosphate + ADP

Ho = standard enthalpies of formation of products - reactants

        = standard enthalpies of formation of [Creatine phosphate + ADP - (Creatine + ATP)]

        = -1510 kJ/mol - 2000 kJ/mol - [ -540 kJ/mol -2982 kJ/mol ]

        = 12 kJ/mol

Ho = 12 kJ/mol

c) Go = Ho - T So

   13.3 kJ/mol = 12 kJ/mol - (298 K)( So)

(298 K) (So) = -1.3 kJ/mol

        So = -0.0044 kJ/mol

Therefore,

So = -0.0044 kJ/mol

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