An immunodetection study of protein tyrosine phosphatase 1B (PTP-1B), SHP-2, and Src in isolated mitochondria from different rat tissues (brain, muscle, heart, liver, and kidney) revealed their exclusive localization in the brain. Given this result, we sought whether mitochondria respond to ATP and to the general tyrosine phosphatase inhibitor orthovanadate and found little or no change in the tyrosine phosphorylation profile of mitochondria from muscle, heart, liver, and kidney. In contrast, ATP induced an enhancement in the tyrosine-phosphorylated protein profile of brain mitochondria, which was further greatly enhanced with orthovanadate and which disappeared when Src was inhibited with two inhibitors: PP2 and PP1. Importantly, we found that in brain mitochondria, ATP addition induced Src autophosphorylation at Tyr-416 in its catalytic site, leading to its activation, whereas the regulatory Tyr-527 site remained unphosphorylated. Functional implications were addressed by measurements of the enzymatic activity of each of the oxidative phosphorylation complexes in brain mitochondria in the presence of ATP. We found an increase in complex I, III, and IV activity and a decrease in complex V activity, partially reversed by Src inhibition, demonstrating that the complexes are Src substrates. These results complemented and reinforced our initial study showing that respiration of brain mitochondria was partially dependent on tyrosine phosphorylation. Therefore, the present data suggest a possible control point in the regulation of respiration by tyrosine phosphorylation of the complexes mediated by Src auto-activation.Mitochondria provide the energy necessary for cell growth and biological activities through oxidative phosphorylation (OxPhos). 4 This relies on electron transfer from oxidative substrates to oxygen, via a series of redox reactions, to generate water. In this process, protons are pumped from the matrix across the mitochondrial inner membrane, via respiratory complexes I, III, and IV. When protons return to the mitochondrial matrix, ATP is synthesized via complex V.As the energy demand of a cell depends on its function and activity, energy production is adjusted and controlled by different mechanisms (1-3). One major regulatory system is protein phosphorylation/dephosphorylation (4). Evidence indicates that mitochondrial proteins undergo posttranslational phosphorylation (2, 5, 6), and reports have unambiguously revealed the existence of several kinases within the mitochondria, such as cAMP-dependent protein kinase (7) and members of the Src kinase family (8). Protein phosphatases have also been described, such as Ser/Thr phosphatases, PP2C-␥ and PP2A (7), and tyrosine phosphatases, SHP-2 (9), PTP-1B (10), and PTPMT1, a dual-specific phosphatase (11), the latter found exclusively in mitochondria but not in the cytosol.As indicated by earlier reports, mitochondrial signaling enzyme distribution and stimulation may vary according to the tissue. In a preceding report, which also explored the presence of PTP...

No abstract