Hydroperoxide-induced loss of pyridine nucleotides and release of calcium from rat liver mitochondria.

It has been previously reported (Lötscher, H. R., Winterhalter, K. H., Carafoli, E., and Richter, C. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 4340-4344) that in Ca2+-loaded mitochondria hydroperoxides induce a release of Ca2+ from mitochondria and an irreversible oxidation of mitochondrial pyridine nucleotides. Here we show that in the presence of Ca2+ oxidized mitochondrial pyridine nucleotides are hydrolyzed inside mitochondria and that nicotinamide is released from mitochondria. The extent of the hydrolysis of NAD(P)+ is dependent on the amount of both hydroperoxide and Ca2+. The hydrolysis is reversible in the presence of added nicotinamide. The release of Ca2+ from mitochondria is electroneutral, and is directly or indirectly dependent on oxidized mitochondrial pyridine nucleotides. By contrast, the uptake of Ca2+ most probably does not require the present of reduced pyridine nucleotides. Control experiments show that even under the most drastic conditions employed in this study (100 nmol of Ca2+ and 85 nmol of t-butylhydroperoxide/mg of protein) mitochondria retain a considerable degree of functional integrity.