Translocation and binding of adenine nucleotides by rat liver mitochondria partially depleted of phospholipids

1. 1. Rat liver mitochondria were partially depleted of their phospholipids using phospholipase A prepared from porcine pancreas (substrate specificity, cardiolipin > phosphatidylethanolamine > phosphatidylcholine) or from Crotalus adamanteus venom (substrate specificity, phosphatidylethanolamine = phosphatidylcholine ⪢ cardiolipin). 2. 2. Removal of only about 1% of the mitochondrial phospholipid with the pancreatic enzyme leads to 50% and 25% losses in ADP and ATP translocation, respectively. Concomitant with the loss in translocation is a decline in the ability of both carbonylcyanide m-chlorophenylhydrazone and Ca2+ to stimulate ATP translocation. 3. 3. To achieve comparable losses in ADP and ATP translocation with the venom enzyme, it is necessary to remove about 8% of the total mitochondrial phospholipid. Following such treatment, carbonylcyanide m-chlorophenylhydrazone and Ca2+ are still capable of stimulating ATP translocation. 4. 4. Control experiments involving treatment of the mitochondria with the products of phospholipase digestion indicate that the effects observed on the translocase reflect a loss of phospholipid from the membrane. 5. 5. Binding studies indicate that the loss in adenine nucleotide translocation following phospholipase treatment cannot be accounted for by an altered ability to bind adenine nucleotides to atractyloside-sensitive sites. 6. 6. The data are interpreted in terms of a mechanism of adenine nucleotide translocation involving a lipoprotein carrier system, consisting of the translocator protein and phospholipids, possibly cardiolipin and phosphatidylethanolamine.