Differential effects of magnesium on the hydrolysis of ADP and ATP in human term placenta: Effect of substrates and potassium

Abstract This study evaluates the effect of Mg 2+ on the extramitochondrial hydrolysis of ATP and ADP by human term placental mitochondria (HPM) and submitochondrial particle (SMP). Extramitochondrial ATPase and ADPase activities were evaluated in the presence or absence of K + , and different oxidizable substrates. Mg 2+ increased both ATP and ADP hydrolysis according to the experimental conditions, and this stimulation was related to the mitochondrial intactness. The ADPase activity in intact mitochondria is 100-fold higher in presence of K + , succinate and 1 mM Mg 2+ while this activity is only increased by two-fold on the SMP when compared to the sample without Mg 2+ . It is clearly demonstrated that up-regulation of these enzyme activities occur in intact mitochondria and not on the enzyme itself. The results suggest that the regulation of ATP and ADP hydrolysis is complex, and Mg 2+ plays an important role in the modulation of the extramitochondrial ATPase and ADPase activities in HPM