DUAL ELECTRON-MICROSCOPIC LOCALIZATION OF MITOCHONDRIAL CREATINE-KINASE IN BRAIN MITOCHONDRIA

Mitochondrial creatine kinase in brain mitochondria appears to be loca ted at two different intramitochondrial sites. By using immunogold-lab eling techniques, a peripheral immunoreactivity was localized between the two boundary membranes, while an additional, central immunoreactiv ity was found at the crista surface. The peripheral enzyme was accessi ble to the antibodies after treatment of the brain mitochondria with 1 00-300 mu g digitonin/mg mitochondrial protein, which left 75% of the activity bound to the membranes. Electron microscopic analyses reveale d that 43% of the labeled, peripheral creatine kinase was bound at tho se places where outer membrane vesicles remained attached to the inner envelope membrane, suggesting that the enzyme is in involved in conta ct formation between outer and inner mitochondrial membranes. Postembe dding staining of mitochondria on thin sections of brain tissue or in the isolated state led to the observation of a second location of crea tine kinase inside the mitochondria, along the cristae, which was not accessible to the antibodies in isolated, digitonin-treated mitochondr ia. (C) 1994 Academic Press, Inc.