Citrate Synthase: The Key Enzyme in the Citric Acid Cycle and its Regulatory Mechanisms

citrate synthase

Couples acetyl-CoA to oxaloacetate and then hydrolyzes the resulting product, forming citrate and CoA-SH. This enzyme is regulated by negative feedback from ATP, NADH, succinyl-CoA, and nitrate

Citrate synthase is a key enzyme involved in the citric acid cycle, which is also called the Krebs cycle or the tricarboxylic acid (TCA) cycle. This enzyme catalyzes the condensation of acetyl-CoA with oxaloacetate to form citrate. The reaction involves the transfer of the acetyl group from acetyl-CoA to oxaloacetate to form a six-carbon intermediate known as citryl-CoA before it is hydrolyzed to form citrate.

The citrate synthase reaction is the first committed step of the citric acid cycle and is therefore a key regulatory step. The enzyme is allosterically regulated, and its activity is influenced by the presence of several metabolites, such as NADH, ATP, and succinyl-CoA. A decrease in NADH concentrations leads to an increase in citrate synthase activity, while an increase in ATP or succinyl-CoA concentrations causes a decrease in the enzyme activity.

The activity of citrate synthase is used as a marker for mitochondrial content in tissues. It is often measured spectrophotometrically and is indicative of the oxidative capacity of the tissue. This measurement is commonly used in sports science to assess an athlete’s training status and to predict performance.

In summary, citrate synthase is a key enzyme in the citric acid cycle, responsible for catalyzing the formation of citrate. The activity of this enzyme is regulated by several metabolites and is used as a marker for mitochondrial content in tissues.

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