Coupling ATP Cleavage to an Unfavorable Reaction To explore the consequences of coupling ATP hydrolysis under...

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Coupling ATP Cleavage to an Unfavorable Reaction To explore the consequences of coupling ATP hydrolysis under physiological conditions to a thermodynamically unfavorable biochemical reac- tion, consider the hypothetical transformation X Y, for which AG" = 20 kJ/mol. (a) What is the ratio [Y]/[X] at equilibrium? (b) Suppose X and Y participate in a sequence of reactions during which ATP is hydrolyzed to ADP and P. The overall reaction is X + ATP + HO Y + ADP + P Calculate [Y][X] for this reaction at equilibrium. Assume that the temperature is 25 C and the equilibrium concentrations of ATP, ADP, and P; are all 1 M. (e) We know that [ATP], [ADP], and [P] are not 1 M under physiological conditions. Calcu- late [Y]/[X] for the ATP-coupled reaction when the values of [ATP], [ADP], and [P;] are those found in rat myocytes (Table 13-5). Coupling ATP Cleavage to an Unfavorable Reaction To explore the consequences of coupling ATP hydrolysis under physiological conditions to a thermodynamically unfavorable biochemical reac- tion, consider the hypothetical transformation X Y, for which AG" = 20 kJ/mol. (a) What is the ratio [Y]/[X] at equilibrium? (b) Suppose X and Y participate in a sequence of reactions during which ATP is hydrolyzed to ADP and P. The overall reaction is X + ATP + HO Y + ADP + P Calculate [Y][X] for this reaction at equilibrium. Assume that the temperature is 25 C and the equilibrium concentrations of ATP, ADP, and P; are all 1 M. (e) We know that [ATP], [ADP], and [P] are not 1 M under physiological conditions. Calcu- late [Y]/[X] for the ATP-coupled reaction when the values of [ATP], [ADP], and [P;] are those found in rat myocytes (Table 13-5).

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