Conformational basis of energy transformations in membrane systems: III. Configurational changes in the mitochondrial inner membrane induced by changes in functional states

Abstract

The cristae of the inner membrane of mitochondria have been shown to exist in three configurational states: nonenergized, energized, and energized-twisted. Electron transfer and hydrolysis of ATP are the two enzymic means of generating the energized state. The transition from the energized to the energized-twisted configurational state of the cristae is induced by inorganic phosphate in sucrose-containing media and by salts in sufficiently high concentrations in media that do not contain sucrose. The electron microscopic identification of the three configurational states is simplified by the diagnostic characteristics of the respective membranes. The configurational states are assumed to be gross expressions of the conformations of the repeating units in the nonenergized, energized, and energized-twisted states. The energized-twisted state is discharged by ADP (leading to oxidative phosphorylation), by divalent metal ions (leading to translocation), by monovalent salts (leading to energized swelling), and by uncouplers. Reagents which inhibit electron transfer or those which inhibit hydrolysis of ATP prevent the generation of the energized state by substrates and by ATP, respectively. The speed of configurational change in the cristae appears to be consistent with the thesis that the primary event in mitochondrial energy transformations is Conformational change of the repeating units. It is proposed that there are no high energy intermediate compounds; also, that the readily demonstrable energized states of the inner membrane are the functional equivalents of the elusive high-energy intermediates.