Simultaneous measurement of oxidative phosphorylation and adenylate kinase in plant mitochondria

An assay system capable of simultaneously measuring ATP, ADP, and AMP concentrations was used for the measurement of oxidative phosphorylation and adenylate kinase (5′-ATP:5′-AMP phosphotransferase) activities in mitochondria which were isolated from etiolated corn, soybean, or cucumber seedlings. Data obtained by this system was correlated with colorimetric P_i uptake and spectrophotometric NADH oxidation measurements. Adenylate kinase was active in both phosphorylating and nonphosphorylating mitochondria. Studies using NaCN, 2,4-dinitrophenol, atractyloside, and 2′-AMP as inhibitors indicated that exogenously supplied ¹⁴C]AMP was converted to ¹⁴C]ADP either by NADH-linked phosphorylation or by translocation and transphosphorylation from intramitochondrial nucleotides.