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  • Title: Quantitative and mechanistic aspects of the hydroperoxide-induced release of Ca2+ from rat liver mitochondria.
    Author: Frei B, Winterhalter KH, Richter C.
    Journal: Eur J Biochem; 1985 Jun 18; 149(3):633-9. PubMed ID: 2988954.
    Abstract:
    We have previously demonstrated in rat liver mitochondria a hydroperoxide-induced hydrolysis of pyridine nucleotides and release of Ca2+ [Lötscher, H. R., Winterhalter, K. H., Carafoli, E. & Richter, C. (1979) Proc. Natl Acad. Sci. USA 76, 4340-4344, and Lötscher, H. R., Winterhalter, K. H., Carafoli, E. & Richter, C. (1980) J. Biol. Chem. 255, 9325-9330]. Here we investigate pyridine nucleotide hydrolysis and Ca2+ release under conditions of minimized Ca2+ cycling and with smaller Ca2+ loads. The extent of pyridine nucleotide hydrolysis, measured by pyridine-nucleotide-derived nicotinamide release from intact mitochondria, and the Ca2+ release rate show a very similar sigmoidal dependence on the mitochondrial Ca2+ load. The hydrolysis of oxidized pyridine nucleotides is limited under non-cycling conditions. Whereas pyridine nucleotide hydrolysis as measured by nicotinamide release is extensive, net loss of mitochondrial pyridine nucleotides is observed only at relatively high Ca2+ loads. Our results indicate the ability of mitochondria to resynthesize pyridine nucleotides after hydrolysis. Neither a decrease of reduced, nor an increase of oxidized, mitochondrial glutathione favour Ca2+ release. From these and previous findings it is concluded that the hydroperoxide-induced Ca2+ release is triggered by a factor which is distal to the oxidation of mitochondrial pyridine nucleotides. Ca2+ release is stimulated when the movement of protons across the inner mitochondrial membrane is facilitated, giving evidence for the operation of the hydroperoxide-induced release pathway as a Ca2+/H+ antiport.
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