Calcium-activated phosphate uptake in contracting corn mitochondria

Abstract

The phosphate inhibition of succinate-powered contraction in corn mitochondria can be reversed with calcium. Associated with this reversal is an accumulation of phosphate and calcium. Both ions are essential for accumulation, although strontium will partially substitute for calcium. Arsenate does not substitute for phosphate except in producing the inhibition of contraction.The antibiotics oligomycin and aurovertin do not block the phosphate inhibition of contraction or the calcium-activated phosphate uptake associated with the release of the inhibition. Dinitrophenol uncouples the phosphate uptake but permits full contraction.Calcium promotes inorganic phosphate accumulation in root tissue as well as in mitochondria.The results are discussed from the viewpoint of theories of calcium reaction with high energy intermediates of oxidative phosphorylation. It is concluded that calcium probably reacts with X approximately P in corn mitochondria, rather than with X approximately I as with animal mitochondria.