Oxidative phase of the pentose cycle
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In addition to AcCoA, propionyl-CoA is also formed by oxidation of odd-chain fatty acids. This is first carboxylated to methylmalonyl-CoA', which is converted to succinyl-CoA - an intermediate of the Krebs cycle'. Through conversion to oxaloacetate, it can participate in gluconeogenesis - glucose can be synthesized from these fatty acids. However, very few fatty acids with an odd number of carbon atoms are found in the body.
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Related Articles[edit | edit source]
- Oxidation of very long chain fatty acids
- Oxidation of unsaturated fatty acids
- Regulation of beta-oxidation of fatty acids
- Lipid breakdown and ketone body metabolism
Source[edit | edit source]
Fontana J., Trnka J., Maďa P., Ivák P. et al.: Transformation of substances and energy in the cell. In: Functions of cells and the human body : Multimedia scripts. Available online from: [1]
The pentose cycle is a catabolic event that provides reduced cofactors NADPH and five-carbon saccharides, or pentoses. It is a metabolic conversion of glucose, the goal of which is not the creation of ATP.
Course of the oxidative phase of the pentose cycle[edit | edit source]
During the oxidative phase of the pentose cycle, the glucose-6-P molecule is oxidized to the ribulose-5-P molecule. At the same time, CO2 is released and two NADPH + H+ molecules are obtained.
Its course is summarized by the following equations:
'Glucose-6-phosphate + 2 NADP+ → CO2 + 2 NADPH+H+ + ribulose-5-phosphate '
Of the reactions of the first phase, the initial reaction catalyzed by ``glucose-6-phosphate dehydrogenase is important. This irreversible reaction is the main regulatory step of the pentose cycle.
The rate of the oxidative phase of the pentose cycle[edit | edit source]
The speed of the entire metabolic pathway depends on the activity of two dehydrogenation reactions, which depend on the availability of NADP+ (i.e. the oxidized form of the coenzyme). With a lack of NADP+, the rate of the pentose cycle decreases, in other words: an excess of NADPH "slows down" the oxidative phase of the pentose cycle.
