EXTRAMITOCHONDRIAL ATP ADP-RATIOS REGULATE CYTOCHROME-C-OXIDASE ACTIVITY VIA BINDING TO THE CYTOSOLIC DOMAIN OF SUBUNIT-IV/

Cytochrome c oxidase from bovine heart contains seven binding sites fo r ATP or ADP and three additional for ADP only, as concluded from comp etition equilibrium dialysis binding studies. The isolated enzyme cont ains bound cholate which, in contrast to bound ATP, is only slowly exc hanged by ADP (or ATP). The kinetics of the reconstituted enzyme is in fluenced by extraliposomal (cytosolic) ATP and ADP. The K-m for cytoch rome c is five times higher in the presence of extraliposomal ATP than of ADP. These differences of K-m values are lost after preincubation of the enzyme with a monoclonal antibody to subunit IV. The data demon strate regulation of cytochrome c oxidase activity by the cytosolic AT P/ADP-ratio, in addition to regulation by the matrix ATP/BDP-ratio [Ar nold and Kadenbach (1997) Eur. J. Biochem.249, 350-354], both interact ing with subunit IV.