Calcium Accumulation by Corn Mitochondria

Corn mitochondria carry out energy-linked Ca^{2 +} accumulationwhen energized in KC1, and Ca^{2 +} release occurs when respirationceases. Stoichiometric H⁺ ejection occurs giving a H⁺: Ca^{2 +}ratio of 0.9 but insensitivity to holmium suggests lack of aCa^{2 +}-specific carrier. Non-energized corn mitochondria contain168 nmol endogenous inorganic phosphate per mg protein, about70 per cent of which is labile to Millipore filtration but stableto centrifugal filtration. Energized mitochondria, collectedby Millipore filtration, show an apparent increase in endogenousinorganic 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 involvementof endogenous Pi. Subsequent Ca²⁺ release occurs despite continuingsubstrate oxidation and is associated with a reduced abilityto synthesize adenosine triphosphate.