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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.
In molecular biology, the citrate synthase family of proteins includes the enzymes citrate synthase EC 2.3.3.1, and the related enzymes 2-methylcitrate synthase EC 2.3.3.5 and ATP citrate lyase EC 2.3.3.8. Citrate synthase is a member of a small family of enzymes that can directly form a carbon-carbon bond without the presence of metal ion ...
The cleft between the CoA binding and citrate synthase domains forms the active site of the enzyme, where both citrate and acetyl-coenzyme A bind. In 2010, a structure of truncated human ATP citrate lyase was determined using X-ray diffraction to a resolution of 2.10 Å. [3]
All of the enzymes for the citric acid cycle are in the matrix (e.g. citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, fumarase, and malate dehydrogenase) except for succinate dehydrogenase which is on the inner membrane and is part of protein complex II in the electron transport chain.
The BCKA decarboxylase enzyme is composed of two subunits in a tetrameric structure (A 2 B 2) and is essential for the synthesis of branched-chain fatty acids. It is responsible for the decarboxylation of α-keto acids formed by the transamination of valine, leucine, and isoleucine and produces the primers used for branched-chain fatty acid ...
Pymol-generated image of E1 subunit of pyruvate dehydrogenase complex in E. Coli. The E1 subunit, called the pyruvate dehydrogenase subunit, is either a homodimer (comprising two “α” chains, e.g. in Escherichia coli) or a heterotetramer of two different chains (two “α” and two “β” chains).
The oxoglutarate dehydrogenase complex has the same subunit structure and thus uses the same cofactors as the pyruvate dehydrogenase complex and the branched-chain alpha-keto acid dehydrogenase complex (TTP, CoA, lipoate, FAD and NAD). Only the E3 subunit is shared in common between the three enzymes. [1]
Oxaloacetate is an intermediate of the citric acid cycle, where it reacts with acetyl-CoA to form citrate, catalyzed by citrate synthase. It is also involved in gluconeogenesis, the urea cycle, the glyoxylate cycle, amino acid synthesis, and fatty acid synthesis. Oxaloacetate is also a potent inhibitor of complex II.