This old version of Proteopedia is provided for student assignments while the new version is undergoing repairs. Content and edits done in this old version of Proteopedia after March 1, 2026 will eventually be lost when it is retired in about June of 2026.
Apply for new accounts at the new Proteopedia. Your logins will work in both the old and new versions.
Krebs cycle step 1
From Proteopedia
First step: Citrate Synthase
Figure: Mechanism of the citrate formation
In the first reaction (see Figure) of the Krebs cycle, acetyl-CoA reacts with oxal acetate. Acetyl-CoA is coupled (yellow background) with the C2 atom of the oxal acetate and the C6 body citryl-CoA is formed. This is a high-energy thioester bound in the enzyme, and it is not released. In the second step of this reaction, the energy-rich thioester is hydrolyzed, and citrate and the coenzyme A (CoA-SH) were formed.
The mechanism of the citrate synthase prevents premature and undesirable hydrolysis of acetyl-CoA, and, consequently, a waste of energy.
