The controlling influence of ADP, ATP and magnesium on the activities of adenylate kinase, ATP synthase, ADP/ATP translocator and the mitochondrial respiration in plants

Abstract

In this study we investigated the influence of adenine nucleotides and magnesium on ATP formation by oxidative phosphorylation and adenylate kinase (AK) and on ATP-export by the ADP/ATP translocator in mitochondria of potato ( Solanum tuberosum L.). Our kinetics and inhibitor studies showed that ATP in mitochondria of potato tubers could be provided by two different enzymes, depending on the ADP concentration. ATP was primarily formed by oxidative phosphorylation at low ADP concentrations and by AK at high ADP concentrations. In addition, the extent of ATP formation and the fractions contributed by each of these two systems were controlled by the level of magnesium ions in the medium. At high magnesium concentrations ADP import, ATP-synthesis by ATP synthase and ATP export increased. The effect of increasing ADP (and ATP) and magnesium concentrations on respiratory rates, respiratory control values and P:O ratios were quantified. Respiration rates of mitochondria from potato tubers in state 3 [B. Chance, G.R. Williams, J. Biol Chem 217 (1955) 635–647] increased with rising ADP (and ATP) concentration, when magnesium was present (5 mM). The P:O ratio was a function of the added ADP but it was independent of the presence of magnesium. Applying the test suggested by Liu et al. [X.C. Liu, K. Jones, H.G. Dickinson, Theor. Appl. Genet. 76 (1988) 305–310] to measure ADP/ATP translocator activity we found some inconsistencies.