Ca2+ transport in mitochondrial and microsomal fractions from higher plants

Abstract

Mitochondria from etiolated corn possess a much greater Ca²⁺ uptake capacity per mg protein than microsomes from the same source. Differences in energy requirements, sensitivity to specific inhibitors, and sedimentation properties enabled us to study both Ca²⁺ uptake mechanisms without mutual contamination. The microsomal Ca²⁺ uptake does not vary much among different plants as compared to the mitochondrial Ca²⁺ uptake; this is also true for different organs of the same plant. Mitochondrial Ca²⁺ uptake is more dependent on the age of the seedlings than microsomal uptake, because of changes in active Ca²⁺ uptake activity rather than of changes in efflux. Intactness and the oxidative and phosphorylative properties of the mitochondria remained unchanged during this time period. Na⁺ and Mg²⁺ do not induce Ca²⁺ release from mitochondria.