At which steps of the Citric Acid Cycle does regulation occur?

In the context of the Citric Acid Cycle, regulation primarily occurs at key enzymatic steps that are critical for the pathway's control over cellular metabolism and energy production. The steps in the cycle that are heavily regulated are primarily associated with irreversible reactions and those influenced by energy needs of the cell.

The first step involves citrate synthase, which catalyzes the condensation of acetyl-CoA with oxaloacetate to form citrate. This reaction is highly regulated by the availability of its substrates (acetyl-CoA and oxaloacetate) and product (citrate), as well as by the energy state of the cell.

The third step is catalyzed by isocitrate dehydrogenase, which converts isocitrate to alpha-ketoglutarate. This enzyme is sensitive to the levels of ADP and NAD+, serving as indicators of cellular energy status, making it an important regulatory point.

Regulation also occurs in the fourth step, where alpha-ketoglutarate dehydrogenase converts alpha-ketoglutarate into succinyl-CoA. This step is regulated similarly to the isocitrate step, being influenced by the levels of products and cofactors like NAD+ and CoA.

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