Comparison with Translocators from Spinach Chloroplasts and Pea Leaf Mitochondria

The kinetic properties of the adenosine 5’-diphosphate/adenosine 5’-triphosphate (ADP/ATP) translocator from pea (Pisum sativum l.) root plastids were determined by silicone oi l filtering centrifugation and compared with those of spinach (Spinacia oleracea 1.) chloroplasts and pea leaf mitochondria. In addition, the ADP/ATP transporting activities from the above organelles were reconstituted into liposomes. l h e K,(ATP) value of the pea root ADP/ATP translocator was 10 p~ and that for ADP was 46 p ~ . Corresponding values of the spinach ADP/ATP translocator were 25 p~ and 28 PM, respectively. Comparable results were obtained for the reconstituted ATP transport activities. l h e transport was highly specific for ATP and ADP. Adenosine 5’-monophosphate (AMP) caused only a slight inhibition and phosphoenolpyruvate and inorganic pyrophosphate caused no inhibition of ATP uptake. With pea root plastids and spinach chloroplasts, K,,, values >1 mM were obtained for ADP-glucose. Since the concentrations of ATP and ADP-glucose in the cytosolic compartment of spinach leaves have been determined as 2.5 and 0.6 mM, respectively, a transport of ADP-glucose by the ADP/ATP translocator does not appear to have any physiological significance in vivo. Although both the plastidial and the mitochondrial ADP/ATP translocators were inhibited to some extent by carboxyatractyloside, no immunological cross-reactivity was detected between the plastidial and the mitochondrial proteins. It seems probable that these proteins derive from different ancestors.