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1. (a) The reaction catalyzed by citrate synthase is the first step of the TCA cycle. In glycolysis, two key reactions to produce ATP occur because an unfavorable reaction is coupled to another reaction that is thermodynamically favorable. The reaction catalyzed by citrate synthase is similarly coupled to an unfavorable reaction in the TCA cycle. Write the unfavorable TCA reaction using structural formulas and write the key step that drives the two coupled reactions forward. What is the overall AG" of the coupled reactions? (b). K(uM) 25.7 Inhibitor Bromoacetyl-CoA ATP NADH 6800 8300 The inhibitor constants for three inhibitors of por- cine citrate synthase are summarized in the table on the right. The compounds were all determined to bind in the ac- tive site as competitive inhibitors of acetyl-CoA. Because they bind as competitive inhibitors, all three inhibitors must exhibit structural similarity to some part of acetyl-CoA. Look up in the textbook the structural formulas for Coenzyme A, ATP, and NADH. What is the largest structural fragment of each inhibitor that is re- sponsible for competitive inhibition? Draw the molecular fragment common to each inhibitor that com- petes with the binding of acetyl-CoA in the active site of citrate synthase. (c)! While the inhibitor constants listed in part (b) above were determined in vitro for purified citrate synthase, does their inhibitory action have any relevance to the flux of metabolites through the TCA cycle in vivo? If so, explain.

1. (a) The reaction catalyzed by citrate synthase is the first step of the TCA cycle. In glycolysis, two key reactions to produce ATP occur because an unfavorable reaction is coupled to another reaction that is thermodynamically favorable. The reaction catalyzed by citrate synthase is similarly coupled to an unfavorable reaction in the TCA cycle. Write the unfavorable TCA reaction using structural formulas and write the key step that drives the two coupled reactions forward. What is the overall AG" of the coupled reactions? (b). K(uM) 25.7 Inhibitor Bromoacetyl-CoA ATP NADH 6800 8300 The inhibitor constants for three inhibitors of por- cine citrate synthase are summarized in the table on the right. The compounds were all determined to bind in the ac- tive site as competitive inhibitors of acetyl-CoA. Because they bind as competitive inhibitors, all three inhibitors must exhibit structural similarity to some part of acetyl-CoA. Look up in the textbook the structural formulas for Coenzyme A, ATP, and NADH. What is the largest structural fragment of each inhibitor that is re- sponsible for competitive inhibition? Draw the molecular fragment common to each inhibitor that com- petes with the binding of acetyl-CoA in the active site of citrate synthase. (c)! While the inhibitor constants listed in part (b) above were determined in vitro for purified citrate synthase, does their inhibitory action have any relevance to the flux of metabolites through the TCA cycle in vivo? If so, explain.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
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1. (a) The reaction catalyzed by citrate synthase is the first step of the TCA cycle. In glycolysis, two key reactions to produce ATP occur because an unfavorable reaction is coupled to another reaction that is thermodynamically favorable. The reaction catalyzed by citrate synthase is similarly coupled to an unfavorable reaction in the TCA cycle. Write the unfavorable TCA reaction using structural formulas and write the key step that drives the two coupled reactions forward. What is the overall AG" of the coupled reactions? (b). K(yM) 25.7 Inhibitor Bromoacetyl-CoA ATP NADH 6800 8300 The inhibitor constants for three inhibitors of por- cine citrate synthase are summarized in the table on the right. The compounds were all determined to bind in the ac- tive site as competitive inhibitors of acetyl-CoA. Because they bind as competitive inhibitors, all three inhibitors must exhibit structural similarity to some part of acetyl-CoA. Look up in the textbook the structural formulas for Coenzyme A, ATP, and NADH. What is the largest structural fragment of each inhibitor that is re- sponsible for competitive inhibition? Draw the molecular fragment common to each inhibitor that com- petes with the binding of acetyl-CoA in the active site of citrate synthase. (c)! While the inhibitor constants listed in part (b) above were determined in vitro for purified citrate synthase, does their inhibitory action have any relevance to the flux of metabolites through the TCA cycle in vivo? If so, explain.
Transcribed Image Text:1. (a) The reaction catalyzed by citrate synthase is the first step of the TCA cycle. In glycolysis, two key reactions to produce ATP occur because an unfavorable reaction is coupled to another reaction that is thermodynamically favorable. The reaction catalyzed by citrate synthase is similarly coupled to an unfavorable reaction in the TCA cycle. Write the unfavorable TCA reaction using structural formulas and write the key step that drives the two coupled reactions forward. What is the overall AG" of the coupled reactions? (b). K(yM) 25.7 Inhibitor Bromoacetyl-CoA ATP NADH 6800 8300 The inhibitor constants for three inhibitors of por- cine citrate synthase are summarized in the table on the right. The compounds were all determined to bind in the ac- tive site as competitive inhibitors of acetyl-CoA. Because they bind as competitive inhibitors, all three inhibitors must exhibit structural similarity to some part of acetyl-CoA. Look up in the textbook the structural formulas for Coenzyme A, ATP, and NADH. What is the largest structural fragment of each inhibitor that is re- sponsible for competitive inhibition? Draw the molecular fragment common to each inhibitor that com- petes with the binding of acetyl-CoA in the active site of citrate synthase. (c)! While the inhibitor constants listed in part (b) above were determined in vitro for purified citrate synthase, does their inhibitory action have any relevance to the flux of metabolites through the TCA cycle in vivo? If so, explain.
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