Plasma membrane Ca-ATPase of radish seedlings. I. Biochemical characterization using ITP as a substrate

• Published in: Plant physiology (Bethesda) Vol. 98; no. 3; pp. 1196 - 1201
• Main Authors: CARNELLI, A, DE MICHELIS, M. I, RASI-CALDOGNO, F
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01-03-1992
• Subjects: actividad enzimatica; activite enzymatique; Adenosine triphosphatases; Biological and medical sciences; calcio; Calcium; Cell membranes; Cell physiology; cell structure; Detergents; Enzymes; enzymic activity; estructura celular; Fundamental and applied biological sciences. Psychology; hidrolasas; hydrolase; hydrolases; Membrane proteins; Plant cells; Plant physiology and development; plantulas; plantule; Plasma membrane and permeation; Radishes; raphanus sativus; Seedlings; structure cellulaire; Vanadates; Vesicle; Ca-ATPase; Calcium; Enzyme; Ion transport; Inorganic element; Raphanus sativus; Enzymatic activity; Cruciferae; Dicotyledones; Substrate specificity; Angiospermae; Plasma membrane; Spermatophyta; Hypoxanthine nucleotide
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.98.3.1196

In this work, we exploited the capability of the plasma membrane Ca-ATPase to utilize ITP as a substrate to study its characteristics in plasma membrane vesicles purified from radish (Raphanus sativus L.) seedlings. The majority of the ITPase activity of plasma membrane was Ca2+-dependent. The Ca2+-dependent ITPase activity was Mg2+-dependent and was stimulated by the calcium ionophore A23187. It was inhibited by erythrosin B (concentration giving 50% inhibition, 50 nanomolar) and by vanadate (concentration giving 50% inhibition, 3 micromolar) and displayed a broad pH optimum around pH 7.2 to 7.5. Both the hydrolytic and the transport activity of the plasma membrane Ca-ATPase were half-saturated by Ca2+ in the micromolar concentration range. No major effect of EGTA on the saturation kinetics of the enzyme was observed. The affinity of the plasma membrane Ca-ATPase for Ca2+ was about fourfold higher at pH 7.5 than at pH 6.9. The Ca2+-dependent ITPase activity was stimulated about twofold by polyoxyethylene 20 cetyl ether, although it was inhibited by Triton X-100 and by lysolecithin.