Studies on the reconstitution of the structure and function of the mitochondrial inner membrane. II. Dissolution and reconstitution of the mitochondrial inner membrane

1) In order to study the molecular structure and electron transfer activities of mitochondrial inner membrane, dissolution and reconstitution of membranous structure and function of the inner membrane of beef heart mitochondria were carried out. 2) The inner membrane of mitochondria could be dissolved into some unit of particles 70-140 &#197; in diameter by the treatment with bile salts at the concentration 0.5 mg of deoxycholate per mg of protein, 0.5 mg of cholate per mg of protein and 74.5 mg of crystalline potassium chloride per ml of the suspension. 3) The dissolved unit particles readily reaggregated into a vesicular membrane simultaneously restoring over-all electron transfer activities by the removal of bile salts with dilution of the suspension.4) Isolated electron transfer unit particle fraction contammg all components of the electron transfer chain but no structural protein were soluble in aqueous solution due to some residual bile salts used in the preparation. The removal of bile salts by dilution led the dispersed particles to aggregate into membrane and restore their over-all enzymatic activities. 5) From these results and the results of the reconstitution of membrane from purified complexes as described in the previous paper, it may be concluded as follows: The mitochondrial inner membrane may consist of several kinds of repeating unit particles conjugating each other with adjacent particles. It is necessary for over·all enzymatic activities that some unit components aggregate into a single vesicular membrane. Structural proteins may play an important role in the constitution of the membranous structure and in the over-all enzymatic activities.</p

Studies on the reconstitution of the structure and function of mitochondrial inner membrane. I. Structure and function of the membrane formed by the purified complex 3 and complex IV of the mitochondrial electron transfer chain

In order to elucidate the molecular organization of mitochondrial inner membrane, biochemical and electron microscope observations were made on the formation of membrane structure and function by the purified complexes of the electron transfer chain of beef heart mitochondria. Purified complex III (CoQ-cytochrome c reductase) and complex IV (cytochrome oxidase) were soluble in the presence of bile salts. They were, however, aggregated to form membrane by washing out the bile salts. When the membranous complexes III and IV were mixed, both membranes were separate by density gradient centrifugation and the vesicle which contained both complexes could not be formed and CoQH2-oxidase activity was hardly re;tored. When the mixture of the solubilized complexes III and IV were diluted to remove the bile salts, a membranous vesicle in which both complexes were assembled was formed. CoQH2-oxidase activity was restored in accordance with the formation of the membrane. The membrane which contained any desired propotion of each complexes could be obtained. These facts indicate that the complexes of the electron transfer chain conjugate two-dimentionally each other and form the membrane to carry electrons from substrate to oxygen most efficiently.</p

Isolation of oligomycin-sensitive adenosine triphosphatase from beef heart mitochondria and analysis of its fine structure

1. An oligomycin -sensitive ATPase was isolated and partially purified from beef heart mitochondria. The specific activity of ATPase sensitive to oligomycin of the fraction was five to eight times that of aged mitochondrial or of DNP-induced mitochondrial ATPase assayed under the same condition. 2. Electron micrographs of the partially purified oligomycin- sensitive ATPase reveal a structure in which headpieces are regularly attached by way of stalks to a thread-like structure derived from a superficial portion of base pieces. 3. A high concentration of the structured material coincided with a high activity of oligomycin-sensitive ATPase. When the headpieces were detached from the structure, the ATPase became insensitive to oligomycin. 4. The fraction of oligomycin -sensitive ATPase was essentially free of membrane structure and was contaminated with a small amount of cytochromes b and Cl but no cyt. a. Cytochrome concentrations of the preparations were indifferent to the activity of oligomycin sensitive ATPase. It follows that ATPase does not require cytochromes or membrane structure for its oligomycin sensitivity. 5. From these results it seems that the factor rendering ATPase sensitive to oligomycin should be contained in the stalks and/or the thread-like portion of basepieces of the structure. The structure is the simplest unit of oligomycinsensitive ATPase as yet obtained. 6. The structure was called &#34;oligomycin-sensitive ATPase particles&#34; (abbreviated as OSA particles). A unit of OSA particles consists of a headpiece attached by a stalk to a portion of base piece.</p

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Role of hydrophobic interaction in hapten-antibody binding

The precipitation reaction of bovine serum albumin coupled with p-azophenylleucine with homologous antibody was inhibited by several structurally related haptens. The isobutyl group substituent on alpha-carbon atom of the leucine residue contributed more than -5.8 Kcal/mol to the free energy of binding. This value was consistent with the free energy change expected from the transfer of n-butane from an aqueous environment to liquid n-butane. The observed contribution was explained, in terms of the hydrophobic interaction of the isobutyl group with the antigen binding site of the antibody molecule. These results were also compared with other hapten-antibody systems.</p