Junpei Asai

Resolution of the repeating unit of the inner mitochondrial membrane

Abstract The tripartite repeating unit of the inner mitochondrial membrane has been resolved into the following components: basepiece, headpiece, and headpiece-stalk. The headpiece contains rutamycin-insensitive ATPase activity; the basepiece contains activities of the electron transfer chain. Ultrastructural and chemical evidence is presented in support of two theses: ( 1 ) the headpiece-stalk sector accounts for the rutamycin-sensitive ATPase function; and ( 2 ) the stalk determines rutamycin sensitivity of the ATPase in the headpiece. An attempt has also been made to bring our observations on the rutamycin-sensitive ATPase and those of E. Racker into accord.

The conformational basis of energy transduction in membrane systems: V. Measurement of configurational changes by light scattering

Abstract Changes in the energy state of the cristal membrane of beef heart mitochondria can be followed continuously by light-scattering measurements at 90 ° to the incident beam. Only two of the three configurational transitions established by electron microscopy can be directly measured by the light-scattering technique. The correlation between the configurational changes deduced from the interpretation of electron micrographs, and the configurational changes implicit in the light-scattering measurements has been tested in a wide spectrum of experiments and found to hold in all cases. It has been concluded that the electron microscopic and light-scattering techniques both measure configurational change in the cristal membrane. The transition of cristae from the aggregated to the orthodox modality, and the oscillation of mitochondria between the energized uptake of K + and swelling, and the de-energized release of K + and shrinking, are phenomena which are readily analyzed by the method of light scattering in combination with that of electron microscopy.

The mechanism of mitochondrial swelling: IV. Configurational changes during swelling of beef heart mitochondria

Abstract Heavy beef heart mitochondria (HBHM) will swell when energized by electron transfer or hydrolysis of ATP in media of appropriate alkali metal salts (energized swelling). Under certain conditions they will also swell in presence of appropriate salts when energized conditions are excluded (pseudoenergized swelling). The configurational changes that underlie both types of large amplitude swelling have been described in terms of several component ultrastructural stages as evidenced by electron microscopic examination. Swelling of either type is characterized by the rapid transition of the mitochondrial inner membrane from the nonenergized to the energized-twisted configuration via the energized configuration. The terminal stages of swelling involve a sequence of configurational changes by which the tubules of the energized-twisted state are expanded and eventually incorporated by coalescence into one vesicular membrane. The rupture of the outer boundary membrane which occurs during the stage of expansion leads to the discharge of the swollen vesicle(s). The sequence and nature of the ultrastructural changes in large amplitude swelling appear to be identical whether the swelling is active, i.e. energized by electron transfer or ATP, or is passive as is the case in the presence of appropriate alkali metal salts.

Reconstitution of the repeating unit of the mitochondrial inner membrane

Abstract The tripartite repeating units of the inner mitochondrial membrane have been reconstituted by interaction either of basepieces with headpieces-stalks, or of basepieces-stalks with headpieces. Reconstitution can be carried out without separating the resolved sectors or, alternatively, by combining the previously isolated sectors. Reconstitution can be recognized by four criteria: (1) a change in the density and sedimentation properties of the product of recombination; (2) the conversion of a soluble ATPase, requiring added phospholipid for activity, into a particulate ATPase which is active in the absence of added lipid; (3) the conversion of a rutamycininsensitive ATPase into a rutamycin-sensitive form; and (4) the visualization by electron microscopy of membranes with projecting headpiece-stalk sectors. Either a mixture of different species of basepieces or isolated single species of basepieces can be used in the reconstitution experiments.

Studies on ultrastructural dislocations in mitochondria: II. On the dislocation induced by lyophilization and the mechanism of uncoupling

Abstract Lyophilization has been shown to uncouple bovine heart mitochondria; however, well-coupled particles may be derived by sonication of the mitochondria uncoupled in this way. An ultrastructural dislocation has been demonstrated by electron microscopy in the cristael membrane of the lyophilized particles. This dislocation is believed to be the morphological basis of uncoupling in lyophilized mitochondria. A mechanism is proposed whereby coupled submitochondrial particles may be derived by sonic irradiation of uncoupled mitochondria.