We have investigated the effects of
hypoxia and
myocardial ischemia/reperfusion on the structure and function of
cytochrome c oxidase (CcO).
Hypoxia (0.1% O(2) for 10 h) and cAMP-mediated inhibition of CcO activity were accompanied by hyperphosphorylation of subunits I, IVi1, and Vb and markedly increased reactive O(2) species production by the
enzyme complex in an in vitro system that uses reduced
cytochrome c as an electron donor. Both subunit phosphorylation and
enzyme activity were effectively reversed by 50 nm
H89 or 50 nm myristoylated
peptide inhibitor (MPI), specific inhibitors of
protein kinase A, but not by inhibitors of
protein kinase C. In rabbit hearts subjected to global and focal
ischemia, CcO activity was inhibited in a time-dependent manner and was accompanied by hyperphosphorylation as in
hypoxia. Additionally, CcO activity and subunit phosphorylation in the ischemic heart were nearly completely reversed by
H89 or MPI added to the perfusion medium. Hyperphosphorylation of subunits I, IVi1, and Vb was accompanied by reduced subunit contents of the immunoprecipitated CcO complex. Most interestingly, both
H89 and MPI added to the perfusion medium dramatically reduced the
ischemia/reperfusion injury to the myocardial tissue. Our results pointed to an exciting possibility of using CcO activity modulators for controlling myocardial injury associated with
ischemia and oxidative stress conditions.