Bovine adrenal cortex mitochondria when isolated in a medium 0·25 M in sucrose contaminated (with calcium) have tubular cristae which are periodically expanded to spherical vesicles and contracted to flattened connecting sections. This scalloped tubular form of the cristae corresponds to the nonenergized orthodox configuration-a configuration in which the matrix space is maximally expanded. When adrenal cortex mitochondria are isolated in media in which the free calcium content is relatively low, e.g., a medium 0·25 M in sucrose and 0·1 mM in EDTA, the cristae assume the aggregated configuration-a nonenergized configuration in which the matrix space is maximally contracted. The composition of the isolation medium determined the configuration. Procedures have been described for isolating bovine adrenal cortex mitochondria (a) predominantly in the orthodox configuration, (b) predominantly in the aggregated configuration, or (c) in a mixed (1:1) population of configurations. The concentration of Ca2+ bound to the mitochondrion was found to be a determinant of the nonenergized configuration. When the level of bound Ca++ was 20-25 μmoles/mg protein, the cristae of the mitochondria were entirely in the orthodox configuration. Addition of Ca2+ could induce the transition of cristae from the aggregated to the orthodox configuration whereas addition of Mg2+ could induce the transition of cristae from the orthodox to the aggregated configuration. The configurational transition could be followed by any of several methods-a change in 90° light scattering, a change in O.D.520 mμ, a change in pH, or examination by electron microscopy. The orthodox to aggregated transition is energy-independent since it proceeds even in presence of inhibitors both of electron transfer and of ATP hydrolysis. The binding of Ca2+ is independent of the binding of Mg2+; this independent binding is consistent with the opposite effects induced by Ca2+ and Mg2+, respectively. Whereas Ca2+ induces a proton release, a decrease in 90° light scattering and a decrease in O.D.520 mμ (when the cristae are initially in the aggregated configuration), Mg2+ induces equal and opposite changes (when the cristae are initially in the orthodox configuration).
ASJC Scopus subject areas
- Cell Biology