Chemistry

Problem

Under standard biochemical conditions (

25\,^{\circ}\!\text{C}

1\,\text{bar}

pH=7

), a chemist must drive the otherwise unfavorable dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP). The dehydration step alone has

\Delta G^{\circ}=+10\,\text{kJ mol}^{-1}

. Table 3 lists three hydrolysis reactions available in the same compartment. Table 3 Potential Hydrolysis Reactions

Reaction	$\Delta G^{\circ}\,(\text{kJ mol}^{-1})$
(1) ATP $^{4-}$ → ADP $^{3-}$ + P $_\text{i}^{2-}$	−30
(2) NTP $^{4-}$ → NDP $^{3-}$ + P $_\text{i}^{2-}$	−28
(3) acetyl phosphate → acetate $^{-}$ + P $_\text{i}^{2-}$	−43

Assuming that each candidate hydrolysis could be enzymatically coupled to the dehydration step through a common phosphate-containing intermediate, (a) Calculate the overall

\Delta G^{\circ}

for coupling the dehydration with each hydrolysis reaction. (b) Identify which hydrolysis reaction yields an overall process that is favorable while wasting the least amount of free energy. State your reasoning. (a) Calculation of overall

\Delta G^{\circ}

for each coupling (b) Selection of optimal hydrolysis reaction with reasoning

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