glyoxysomes

Glyoxysomes are specialized peroxisomes found in plants and some microorganisms. They function as sites of the glyoxylate cycle, a metabolic pathway that enables the conversion of stored fats into carbohydrates during seed germination and in lipid-rich tissues.

Biochemical features include the beta-oxidation of fatty acids within the glyoxysome to produce acetyl-CoA, and the operation of the glyoxylate cycle itself. The cycle bypasses the decarboxylation steps of the tricarboxylic acid (TCA) cycle through the enzymes isocitrate lyase and malate synthase, yielding succinate and malate. These molecules can then be used for gluconeogenesis, providing carbon skeletons for growth in non-photosynthetic tissues or before photosynthesis is established. In addition, glyoxysomes retain typical peroxisomal functions, such as catalase activity, and share components of beta-oxidation with other peroxisomes.

Biological role and development are most prominent during seed germination in oil-storing seeds. The glyoxylate cycle allows the plant to convert lipid reserves into sugar precursors that support seedling growth until photosynthesis can supply energy and carbon. In mature photosynthetic tissues, glyoxysomal activity declines as carbohydrate production shifts toward photosynthetic pathways, and peroxisomal metabolism adapts accordingly.

Distribution and evolution: glyoxysomes are characteristic of higher plants’ seeds and certain microorganisms; animals lack a glyoxylate cycle and rely on different metabolic strategies. Glyoxysomes are considered a specialized subclass of peroxisomes dedicated to lipid-derived carbon conversion.