Glyoxylate cycle

Glyoxylate cycle is a metabolic pathway that occurs in many bacteria, plants, and fungi. It is a variation of the citric acid cycle and allows these organisms to survive on acetate or fatty acids as the sole carbon source. The glyoxylate cycle bypasses the decarboxylation steps of the citric acid cycle and, thus, conserves the carbons of isocitrate to form glyoxylate and succinate.

Overview

The glyoxylate cycle begins in the mitochondria, where two molecules of acetyl-CoA condense to form citrate via the enzyme citrate synthase. This citrate is then converted to isocitrate by aconitase.

In the next step, isocitrate is converted into glyoxylate and succinate by the enzyme isocitrate lyase. This is the first unique step of the glyoxylate cycle. The glyoxylate is then condensed with another molecule of acetyl-CoA to form malate, catalyzed by the enzyme malate synthase. This is the second unique step of the glyoxylate cycle.

The malate is then converted back to oxaloacetate by malate dehydrogenase, completing the cycle. The oxaloacetate can then be used to initiate another round of the cycle.

Role in Organisms

The glyoxylate cycle is crucial for many organisms as it allows them to grow on acetate or fatty acids as the sole carbon source. This is particularly important for plants and fungi, which often have to survive in environments where carbohydrates are scarce.

See Also

• Citric acid cycle
• Acetate
• Fatty acid
• Mitochondria
• Citrate synthase
• Aconitase
• Isocitrate lyase
• Malate synthase
• Malate dehydrogenase

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