Which of the following steps produces GTP in the Citric Acid Cycle?

In the Citric Acid Cycle, the production of GTP occurs during the conversion of succinyl-CoA to succinate, which takes place in a specific step of the cycle. This reaction is catalyzed by the enzyme succinyl-CoA synthetase (or succinate thiokinase). During this process, the high-energy thioester bond in succinyl-CoA is hydrolyzed, facilitating the phosphorylation of GDP (guanosine diphosphate) to GTP (guanosine triphosphate).

The importance of GTP lies in its role as a high-energy molecule that can readily be converted to ATP, thus linking the citric acid cycle with cellular energy metabolism. This conversion is an example of substrate-level phosphorylation, highlighting a direct energy yield within the cycle.

Understanding why this specific step produces GTP helps in comprehending the overall energy balance and metabolic functions of the citric acid cycle, which is crucial for cellular respiration and metabolism.