Calcium Accumulation by Corn Mitochondria

Abstract

Corn mitochondria carry out energy-linked Ca^{2 +} accumulation when energized in KC1, and Ca^{2 +} release occurs when respiration ceases. Stoichiometric H⁺ ejection occurs giving a H⁺: Ca^{2 +} ratio of 0.9 but insensitivity to holmium suggests lack of a Ca^{2 +}-specific carrier. Non-energized corn mitochondria contain 168 nmol endogenous inorganic phosphate per mg protein, about 70 per cent of which is labile to Millipore filtration but stable to centrifugal filtration. Energized mitochondria, collected by Millipore filtration, show an apparent increase in endogenous inorganic phosphate content concurrent with Ca²⁺ accumulation, both of which are inhibited by mersalyl. Accumulation of Ca²⁺ also occurs in a potassium acetate medium but without involvement of endogenous Pi. Subsequent Ca²⁺ release occurs despite continuing substrate oxidation and is associated with a reduced ability to synthesize adenosine triphosphate.