Glyoxysome

Glyoxysomes are specialized peroxisomes found in plants (particularly in the germinating seeds of fat-storing plants) and also in filamentous fungi. They contain enzymes for the glyoxylate cycle which allows them to convert fats into sugars.

Function

The main function of glyoxysomes is to convert stored lipids into carbohydrates during germination of a seed. This is done through the glyoxylate cycle, which bypasses the decarboxylation step of the citric acid cycle and makes it possible for the organism to convert fatty acids to carbohydrates.

Structure

Glyoxysomes, like peroxisomes, are bound by a single membrane. They are small organelles, typically 0.5 to 1.0 micrometer in diameter. They contain a dense matrix that includes the enzymes of the glyoxylate cycle.

Glyoxylate Cycle

The glyoxylate cycle is a variation of the citric acid cycle. It is a metabolic pathway occurring in plants and bacteria and is catalyzed by the enzymes in glyoxysomes. The glyoxylate cycle allows these organisms to convert fatty acids into carbohydrates.

Enzymes

Glyoxysomes contain several enzymes that are involved in the glyoxylate cycle. These include isocitrate lyase and malate synthase. Isocitrate lyase catalyzes the cleavage of isocitrate to glyoxylate and succinate, while malate synthase catalyzes the condensation of glyoxylate and acetyl-CoA to form malate.

See Also

• Peroxisome
• Glyoxylate cycle
• Citric acid cycle
• Isocitrate lyase
• Malate synthase