Propriétés des activités ATPasiques mitochondriales et microsomales de l'épicotyle de Pois: Properties of Mitochondrial and Microsomal ATPase Activities of Pea Epicotyls

Abstract

Summary Homogeneous mitochondrial and enriched plasma-membrane microsomal fractions were obtained from Pea epicotyl by layering crude fractions onto a five-layer discontinuous density gradient of Percoll. After purification, the activity of the monovalent-ion-stimulated ATPase in mitochondria was increased two fold and that of microsomes by 10. Two types of Mg2+-dependent ATPase activities were detected: one, stimulated by monovalent ions and another, partially eliminated by purification, insensitive to monovalent ions. Mitochondrial and microsomal ATPase activities were characterized on the basis of optimal pH, sensitivity to mono- and divalent ions, and substrate specificity. Na+ and K+ had no synergistic effect on mitochondrial and microsomal ATPase activities which were ouabain insensitive. Mitochondrial Mg2+-dependent ATPase activity is inhibited by oligomycin which had no effect of Na+ and K+-ATPase activity. On the contrary, the microsomal monovalent-ion-stimulated ATPase activity was inhibited by vanadate. Substrate specificity as well as 50 % of the two ATPase activities were preserved after paraformaldehyde fixation for 30 min.