Phosphorylation system

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Phosphorylation system


From Gnaiger 2014 MitoPathways

The phosphorylation system is the functional unit utilizing the protonmotive force to phosphorylate ADP (D) to ATP (T), and may be defined more specifically as the phosphorylation system or P»-system. The P»-system consists of adenine nucleotide translocase, phosphate carrier, and ATP synthase. Mitochondrial adenylate kinase, mt-creatine kinase and mt-hexokinase constitute extended components of the P»-system, controlling local AMP and ADP concentrations and forming metabolic channels. Since substrate-level phosphorylation is involved in the TCA-cycle, the P»-system includes succinyl-CoA ligase (GDP to GTP or ADP to ATP).

Abbreviation: DT

Reference: Gnaiger 2009 Int J Biochem Cell Biol

MitoPedia concepts: MiP concept, SUIT concept 

MitoPedia topics: Enzyme 

Communicated by Gnaiger E 2010-08-15, edited 2018-01-04, 2016-08-26.

OXPHOS and substrate level phosphorylation

OXPHOS capacity, measured as oxygen flux in coupled, ADP- and Pi-saturated mitochondria in an electron transfer-pathway state, may be limited by the capacity of the phosphorylation system. Mitochondria are the location of the chemiosmotic P»-system, but additionally carry out substrate-level phosphorylation in the TCA-cycle at the step of succinyl-CoA ligase, phosphorylating GDP to GTP or ADP to ATP (taken together as P»). This step must be considered in the P»-system. If succinate is externally added to mt-preparations, succinyl-CoA ligase is not involved. However, if succinate is formed in the mt-matrix from 2-oxoglutarate (alpha-ketoglutarate), substrate-level phosphorylation at succinyl-CoA ligase must be accounted for in the interpretation of P/O2 ratios.