Effects of ionic strength and sulfhydryl reagents on the binding of creatine phosphokinase to heart mitochondrial inner membranes.

The concept that creatine phosphokinase is bound to the outer surface of the heart mitochondrial inner membrane originated from observations that the enzyme is retained by water-swollen heart mitochondria and by digitonin-treated heart mitochondria suspended in isotonic sucrose. The present study establishes that digitonin-treated mitochondria release creatine phosphokinase in isotonic KCl, and other investigators have reported an identical response for the water-swollen organelles. These observations suggest that mitochondrial creatine phosphokinase is not bound to the outer surface of the inner membrane at a site adjacent to the adenine nucleotide translocase under physiologic conditions.