Citric Acid (Citrate)

Citrate is a citric acid cycle (and glyoxylate cycle) intermediate (reactions 1 and 2 below)

1. Acetyl-CoA + Oxaloacetate <=> Citrate + CoASH (catalyzed by Citrate Synthase)

2. Citrate <=> cis-aconitate <=> D-Isocitrate (catalyzed by Aconitase)

3. Citrate + ATP + CoASH <=> Acetyl-CoA + Oxaloacetate + ADP + Pi (catalyzed by Citrate Lyase)

In the first reaction, citroyl-CoA is a transient intermediate and in the second reaction, cis-aconitate is a tranient intermediate. Citrate is used in fatty acid biosynthesis to transport acetyl-CoA across the mitochondrial membrane to the cytoplasm (Figure 18.31). After release in the cytoplasm, reaction #3 occurs.

Citrate acts allosterically to stimulate polymerization of acetyl-CoA carboxylase (regulatory enzyme for fatty acid biosynthesis) and inhibits the glycolysis enzyme, phosphofructokinase.

See also: Citric Acid Cycle, Glyoxylate Cycle

INTERNET LINKS:

> 1. Glyoxylate Cycle Metabolism

> 2. Citric Acid Cycle