Correlation of structure and function in the oxidative phosphorylation system of submitochondrial particles

1. After the centrifugation of sonicated heavy beef heart mitochondria at 75, 000 × g for 10 minutes, the supernatant was centrifuged at 144, 000 × g for 30 minutes. The residue was revealed being composed of vesicular inner membrane fragments (ETPH), about 600 to 1000 Å. in diameter, showing a morphological homogeneity and a high capacity of oxidative phosphorylation. 2. The Pia ratio of the ETPH in the presence of succinate and of NADH2 was 1.68 and 2.54, respectively, and the corrected Pia value for O2 gas equilibrium was 1. 01 and 1.40, respectively. 3. The capacity of oxidative phosphorylation in ETPH fraction was parallel to the activity of the oligomycin. sensitive ATPase in these fractions. 4. The P/0 ratio of ETPH was decreased to about 50 % by hypotonic treatment. The decrease of P/0 ratio was restored to the level of about 90 % by incubating the ETPH with ATP and BSA. In the instance where the P/0 ratio was low level in the hypotonic medium, the surface structure of ETPH was observed as a swollen form and the head pieces of the elementary particles were clearly observed in contrast to the solid surface structure of ETPH in the isotonic medium. 5. The P/0 ratio of ETPH was decreased to about 60 % by relatively severe sonication, and after separating the residue from the supernatant, that of the residue decreased further to about 40 %. The P/0 ratio of the residue was restored to the level before the separation on the addition of the supernatant containing oligomycin-insensitive ATPase. 6. A discussion was made on the correlation between the surface structure and the activities at terminal phosphorylation step of ETPH after the simple physico-chemical treatment.