The Glyoxylate Cycle A Related Pathway

In plants and in some bacteria, but not in animals, acetyl-GoA can serve as the starting material for the biosynthesis of carbohydrates. Animals can convert carbohydrates to fats, but not fats to carbohydrates. (Acetyl-GoA is produced in the catabolism of fatty acids.) Two enzymes are responsible for the ability of plants and bacteria to produce glucose from fatty acids. Isocitrate lyase cleaves isocitrate, producing glyoxylate and succinate. Malate synthase catalyzes the reaction of glyoxylate with acetyl-GoA to produce malate. 

The reaction of glyoxylate with acetyl-GoA to produce malate 

This pathway results in the net conversion of two acetyl-CoA to oxaloacetate. All the reactions are shown in purple. The unique reactions of the glyoxylate cycle are shown with a light green highlight in the center of the circle. 

The glyoxylate cycle also occurs in bacteria. This point is far from surprising because many types of bacteria can live on very limited carbon sources. They have metabolic pathways that can produce all the biomolecules they need from quite simple molecules. The glyoxylate cycle is one example of how bacteria manage this feat. 

In plants and bacteria, the glyoxylate cycle is a pathway that bypasses the two oxidative decarboxylations of the citric acid cycle. As a result of this pathway, plants can convert acetyl-CoA to carbohydrates, which animals cannot do. 

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The Glyoxylate Cycle A Related Pathway The Citric Acid Cycle in Cataholism... 

In Chapters 9 and 13, other related pathways are discussed. Photosynthesis, a process in which light energy is captured to drive carbohydrate synthesis, is described in Chapter 13. In Chapter 9 the glyoxylate cycle is considered. In the glyoxylate cycle some organisms (primarily plants) manufacture carbohydrate from fatty acids. 

In plants and hacteria, there is a pathway related to the citric acid cycle the glyoxylate cycle. The two oxidative decarboxylations of the citric acid cycle are bypassed. This pathway plays a role in the ability of plants to convert acetyl-GoA to carbohydrates, a process that does not occur in animals. 

Elucidation of the metabolic pathway repertoire of C, glutamicum was initiated soon after its discovery [4-6], related to the high importance of the central metabolism for amino acid fermentation. Evidence on the presence of the major catabolic routes, such as the Embden-Meyerhof-Parnas (EMP) pathway, the pentose phosphate (PP) pathway, the tricarboxylic acid (TCA) cycle, and the glyoxylate shunt had already been provided by the end of the 1950s [4, 5, 7] (Figure 6.1). However, it took more than 30 years for a more detailed resolution of the central metabolic network mainly related to the complex structure of the phosphoenolpyruvate/pyruvate - oxaloacetate/malate node [8-11]. Altogether,... 

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