glyoxylate cycle

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glyoxylate cycle A metabolic pathway in plants and microorganisms that is a modified form of the Krebs cycle. It utilizes fats as a source of carbon and enables the synthesis of carbohydrate from fatty acids by avoiding the stages of the Krebs cycle in which carbon dioxide is released. It occurs in tissues rich in fats, such as those of germinating seeds; the enzymes involved in the cycle, which have not been found in mammals, are contained in organelles (microbodies) called glyoxysomes. The glyoxylate cycle differs from the Krebs cycle in that it utilizes two molecules of acetyl coenzyme A (rather than one), which are derived from fatty-acid oxidation. Isocitrate is converted to succinate (from which glucose can be synthesized in gluconeogenesis) and glyoxylate (see illustration).