glyoxylate metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving glyoxylate, the anion of glyoxylic acid, HOC-COOH. [ISBN:0198506732]

The glyoxylate cycle is a metabolic pathway that enables plants, bacteria, fungi, and some protists to grow on two-carbon compounds like acetate. This cycle is a modification of the tricarboxylic acid (TCA) cycle, where the decarboxylation steps are bypassed, allowing the net synthesis of four-carbon compounds.

**Key Features:**

* **Bypass of Decarboxylation:** The glyoxylate cycle bypasses the decarboxylation steps of the TCA cycle, conserving carbon for biosynthesis.
* **Isocitrate Lyase and Malate Synthase:** Two key enzymes, isocitrate lyase and malate synthase, are unique to the glyoxylate cycle.
* **Anaplerotic Role:** This cycle serves as an anaplerotic pathway, replenishing intermediates of the TCA cycle.

**Steps:**

1. **Acetyl-CoA Entry:** The cycle begins with the entry of acetyl-CoA, derived from the breakdown of two-carbon compounds like acetate.
2. **Citrate Formation:** Acetyl-CoA combines with oxaloacetate to form citrate, similar to the TCA cycle.
3. **Isocitrate Formation:** Citrate is converted to isocitrate through the action of aconitase.
4. **Isocitrate Cleavage:** Isocitrate lyase cleaves isocitrate into glyoxylate and succinate.
5. **Malate Formation:** Glyoxylate reacts with acetyl-CoA in the presence of malate synthase to form malate.
6. **Oxaloacetate Regeneration:** Malate is oxidized to oxaloacetate, which can be used to continue the cycle or for biosynthesis.

**Significance:**

* **Growth on Acetate:** The glyoxylate cycle enables organisms to utilize acetate, a key carbon source for many microorganisms and plants.
* **Seed Germination:** In plants, the glyoxylate cycle plays a crucial role during seed germination, providing energy and building blocks for growth.
* **Fatty Acid Metabolism:** The cycle is important for fatty acid metabolism, converting fatty acids into carbohydrates.
* **Pathogenicity:** In some pathogenic bacteria, the glyoxylate cycle is involved in virulence and persistence within the host.

**Regulation:**

The glyoxylate cycle is tightly regulated, ensuring its activation only when necessary. Key regulatory mechanisms include:

* **Substrate Availability:** The cycle is activated by the presence of acetate and other two-carbon compounds.
* **Enzyme Regulation:** Isocitrate lyase and malate synthase are subject to transcriptional and post-translational regulation.
* **Metabolic Context:** The activity of the glyoxylate cycle is influenced by other metabolic pathways and cellular conditions.'
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