Substrate-level phosphorylation
2027148
216568286
2008-06-02T06:31:13Z
MiPe
2036281
'''Substrate-level phosphorylation''' is a type of [[chemical reaction]] that results in the formation of [[adenosine triphosphate]] (ATP) by the direct transfer of a [[phosphate]] group to [[adenosine diphosphate]] (ADP) from a [[reactive intermediate]]. In [[cell (biology)|cells]], it occurs in the [[cytoplasm]] (in [[glycolysis]]) under both [[wikt:aerobic|aerobic]] and [[wikt:anaerobic|anaerobic]] conditions.
Unlike [[oxidative phosphorylation]], here the [[oxidation]] & [[phosphorylation]] is not coupled.
In the [[Glycolysis#Pay-off_phase|pay-off phase of glycolysis]], four ATP are produced by substrate-level phosphorylation: two [[1,3-bisphosphoglycerate]] are converted to [[3-phosphoglycerate]] by [[transferase|transferring]] a phosphate group to ADP by the enzyme phosphoglycerate kinase; two [[phosphoenolpyruvate]] are converted to [[pyruvate]] by the transfer of their phosphate groups to ADP by the enzyme pyruvate kinase.
In the [[citric acid cycle]], one [[guanosine triphosphate]] (GTP) (which can donate a phosphate group to ADP or UDP, forming the respective triphosphates (a near equilibrium reaction catalyzed by nucleoside diphosphate kinase)) is produced by substrate-level phosphorylation (per cycle, with 2 cycles per glucose molecule) when [[succinyl-CoA synthetase]] converts [[succinyl-CoA]] to [[succinate]].
Substrate-level phosphorylation is also seen in working skeletal muscles and the brain. [[Phosphocreatine]] is stored as a readily available high-energy phosphate supply, and the enzyme [[creatine phosphokinase]] transfers a phosphate from phosphocreatine to ADP to produce ATP. Then the ATP releases giving chemical energy.
An alternative way to create ATP is through [[oxidative phosphorylation]], which takes place during the process of aerobic [[cellular respiration]], in addition to the substrate-level phosphorylation that occurs during glycolysis and the Krebs cycle. During oxidative phosphorylation NADH is oxidized to NAD+ yielding 2.5 ATPs, and FADH2 yields 1.5 ATPs when it is oxidized.
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[[Category:Cellular respiration]]
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