Citrate synthase's 437 amino acid residues are organized into two main subunits, each consisting of 20 alpha-helices.
 These alpha helices compose approximately 75% of citrate synthase's tertiary structure, while the remaining residues mainly compose irregular extensions of the structure, save a single beta-sheet of 13 residues.
 Between these two subunits,  a single cleft exists containing the active site.
 Two binding sites can be found therein: one reserved for citrate or oxaloacetate and the other for Coenzyme A.  The active site contains three key residues: His274, His320, and Asp375 that are highly selective in their interactions with substrates.

The adjacent images display the tertiary structure of citrate synthase in its opened and closed form.
 The enzyme changes from opened to closed with the addition of one of its substrates (such as oxaloacetate).
Citrate synthase's 437 amino acid residues are organized into two main subunits, each consisting of 20 alpha-helices.  These alpha helices compose approximately 75% of citrate synthase's tertiary structure, while the remaining residues mainly compose irregular extensions of the structure, save a single beta-sheet of 13 residues.  Between these two subunits,  a single cleft exists containing the active site.  Two binding sites can be found therein: one reserved for citrate or oxaloacetate and the other for Coenzyme A.  The active site contains three key residues: His274, His320, and Asp375 that are highly selective in their interactions with substrates.
The adjacent images display the tertiary structure of citrate synthase in its opened and closed form.  The enzyme changes from opened to closed with the addition of one of its substrates (such as oxaloacetate).
Citrate synthase