Incorporation of N-ethylmaleimide into the membrane-bound ADP/ATP translocator. Isolation of the protein labeled with N-[3H]ethylmaleimide.

The incorporation of N-ethylmaleimide into the 30,000-Mr component of beef-heart mitochondria has been studied as a function of various ligands to the ADP/ATP carrier and the isolation of the N-ethylmaleimide-labeled protein is reported. 1. The incorporation of N-ethylmaleimide into the 30,000-Mr component is specifically stimulated by ADP and ATP. Thus by differential incorporation of N-ethylmaleimide, the 30,000-Mr component is preferentially labeled. 2. Addition of carboxyatractylate inhibits, whereas bongkrekate tolerates, the incorporation of N-ethylmaleimide. 3. After solubilization by Triton the purification of N-ethylmaleimide-labeled protein is facilitated in the presence of bongkrekate but not of carboxyatractylate, in agreement with the postulated existence of only a bongkrekate-N-ethylmaleimide-protein complex. The labeled protein was purified to homogeneity on hydroxyapatite in Triton and subsequently, after denaturation in dodecylsulfate, on Sepharose 6B. 4. The identify of the isolated labeled protein with the formerly isolated bongkrekate-protein or carboxyatractylate-protein complexes is confirmed by the isoelectric point and amino acid composition. 5. Two moles of N-ethylmaleimide must be incorporated into the 30,000-Mr component in order to inhibit fully the binding of one mole carboxyatractylate. This corresponds to one -SH group per unit.