Some effects of Ca 2+, Mg 2+, and Mn 2+ on the ultrastructure, light-scattering properties, and malic enzyme activity of adrenal cortex mitochondria

Abstract

The ultrastructure and 90 ° light-scattering capacity of adrenal cortex mitochondria have been examined under conditions which lead to an activation of malic enzyme activity in these mitochondria. After isolation, the mitochondria display an aggregate ultrastructure which does not resemble the vesicular (orthodox) form normally seen in vivo. Under conditions of malic enzyme activation (presence of malate, NADP +, Mg 2+ and 1 m m Ca 2+), the ultrastructure reverts to a vesicular form as seen in vivo. Of these required components, only Ca 2+ affects the ultrastructure. The ultrastructural transformation from the aggregate to the orthodox form is always accompanied by a decrease in the 90 ° light-scattering capacity. When produced by Ca 2+, transformation requires energy-dependent Ca 2+ uptake if an oxidizable substrate is present. In the absence of substrate, the transformation occurs as an apparent energy-independent effect. Mn 2+ can substitute for Ca 2+ only in the presence of substrate. In de-energized mitochondria, Mn 2+ prevents the effects of Ca 2+. The activation of malic enzyme is always preceded by a decrease in light scattering and transformation to the orthodox ultrastructure; however, the presence of the orthodox form is not a sufficient condition since subsequent chelation of free Ca 2+ fails to reverse either the decrease in light scattering or ultrastructural transformation but does reverse the enzyme activation. In addition, levels of Mn 2+ which effectively depress light-scattering capacity and produce the orthodox form, fail to activate malic enzyme significantly. The data are discussed as they relate to Ca 2+-induced damage in mitochondria.