1. One of the chemical steps in the metabolism of
carbohydrates is the conversion of phosphoenolpyruvate
(PEP) to pyruvate. This reaction releases energy, which
is used to synthesize ATP from ADP. The overall
reaction is shown below:
PEP + ADP $\rightleftharpoons$ pyruvate + ATP $K_{eq}$ = 3.21x10⁵
If the equilibrium constant for the hydrolysis of ATP is
2.23 x 10⁵, what is the equilibrium constant for the
conversion of PEP + H₂O to pyruvate + P₁?
2. Lactate dehydrogenase catalyzes the conversion of
pyruvate to lactic acid. This reaction converts NADH to
NAD⁺ and is essential under conditions where anaerobic
metabolism occurs (e.g. during exercise). Suppose you
have a patient that has a defective form of lactate
dehydrogenase and, as a result, is unable to catalyze the
conversion of pyruvate into lactic acid. Since this patient
can't get rid of pyruvate by converting it to lactic acid,
pyruvate will build up under conditions where anaerobic
metabolism occurs. The accumulation of pyruvate will
affect the conversion of PEP + ADP to pyruvate + ATP.
If the ratio of products (ATP + pyruvate) to substrates
(PEP + ADP) is 100:1, what is the free energy (ΔG<sub>rxn</sub>) for
the conversion of PEP + ADP to pyruvate + ATP? Do
these conditions favor the formation of ATP or PEP?
(R=8.31 J/K-mol, T=298 K, K<sub>eq</sub> = 3.21 x 10⁵ for PEP +
ADP $\rightleftharpoons$ pyruvate + ATP).
