Temperature Dependence of ADP/ATP Translocation in Mitochondria

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Abstract
The temperature dependence of the adenine nucleotide exchange in mitochondria was determined by employing a rapid mixing, quenching and sampling apparatus and the inhibitor quench-back exchange method. Thus, the exchange is resolved down to 0.1 s. Rates are evaluated from accumulating the time-dependent progress at about 10 points. The exchange rate in liver mitochondria was determined from -10.degree. C to +10.degree. C in the presence of 20% glycol, from 0.degree. C to 25.degree. C, and from 20.degree. C to 40.degree. C under partial inhibition by carboxyatractylate. The total range between -10.degree. C to +40.degree. C has only 1 temperature break at 13.degree. C. From the Arrhenius plot between -10.degree. C to +13.degree. C, EA [activation energy] .apprxeq. 140 kJ and above 13.degree. C, EA .apprxeq. 56 kJ is evaluated, corresponding to a Q10 of 8 and 2 respectively. In beef heart mitochondria the exchange rate was measured between 0.degree. C and 20.degree. C, and between 15.degree. C and 30.degree. C under partial inhibition with carboxyatractylate. There is a temperature break around 14.degree. C with EA .apprxeq. 143 kJ between 0.degree. C and 14.degree. and EA .apprxeq. 60 kJ from 15.degree. C to 30.degree. C. The extrapolated translocation rates at 37.degree. C are 500 and 1800 .mu.mol min-1 (g protein)-1 for rat liver and for beef heart mitochondria respectively. The temperature break probably reflects a conformation change since there is no reversed break at low temperature, the temperature break changes in sonic particles and no lipid phase transition at 14.degree. C in mitochondria has been reported.