Description
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 DT-phosphorylation system or DT-system. The DT-system consists of adenylate nucleotide translocase, phosphate carrier, and ATP synthase. Mitochondrial adenylate kinase, mt-creatine kinase and mt-hexokinase constitute extended components of the DT-phosphorylation system, controlling local AMP and ADP concentrations and forming metabolic channels. Since substrate-level phosphorylation is involved in the TCA-cycle, the mtDT system includes succinyl-CoA synthase (GDP to GTP or ADP to ATP).
Abbreviation: DT
Reference: Gnaiger 2009 Int J Biochem Cell Biol
MitoPedia concepts:
Respiratory state
MitoPedia topics:
Enzyme
Author: Gnaiger E (last edit: 2014-07-07)
OXPHOS and substrate level phosphorylation
OXPHOS capacity, measured as oxygen flux in coupled, ADP- and Pi-saturated mitochondria in an ETS-competent substrate state, may be limited by the phosphorylation system capacity. Mitochondria are the location of the chemiosmotic DT-system, but additionally carry out substrate-level phosphorylation in the TCA-cycle at the step of succinyl-CoA synthase, phosphorylating GDP to GTP or ADP to ATP (taken together as DT). This step must be considered in the mtDT-phosphorylation system. If succinate is externally added to mt-preparations, succinyl-CoA synthase is not involved. However, if succinate is formed in the mt-matrix from 2-oxoglutarate (alpha-ketoglutarate), substrate-level phosphorylation at succinyl-CoA synthase must be accounted for in the interpretation of P/O (P/O2) ratios.