Identification and characterization of the Ca2+ -ATPase which drives active transport of Ca2+ at the plasma membrane of radish seedlings

• Published in: Plant physiology (Bethesda) 1989-08, Vol.90 (4), p.1429-1434
• Main Authors: Rasi-Caldogno, F. (Universita di Torino, Torino, Italy), Pugliarello, M.C, Olivari, C, De Michelis, M.I
• Format: Article
• Language: English
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Biological and medical sciences; CALCIO; CALCIUM; ECHANGE D'ION; Enzymes; ESTRUCTURA CELULAR; Fundamental and applied biological sciences. Psychology; HIDROLASAS; HYDROLASE; INTERCAMBIO IONICO; Membranes and Bioenergetics; Metabolism; Plant physiology and development; PLANTULAS; PLANTULE; RAPHANUS SATIVUS; STRUCTURE CELLULAIRE
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.90.4.1429

In microsomes from 24-hour-old radish (Raphanus sativus L.) seedlings ATP-dependent Ca2+ uptake occurs only in inside-out plasma membrane vesicles (F Rasi-Caldogno, MC Pugliarello, Ml De Michelis [1987] Plant Physiol 83:994-1000). A Ca2+ -dependent ATPase activity can be shown in the same microsomes, when assays are performed at pH 7.5. The Ca2+ -dependent ATPase is stimulated by the Ca2+ ionophore A23187 and is localized at the plasma membrane. Ca2+ -dependent ATPase activity and ATP-dependent Ca2+ uptake present very similar saturation kinetics with erythrosin B (50% inhibition at about 0.1 micromolar), free Ca2+ (half-maximal rate at about 70 nanomolar), and MgATP (Km 15-20 micromolar). Ca2+ uptake can be sustained by GTP or ITP at about 60% the rate measured in the presence of ATP; only very low Ca2+ uptake is sustained by CTP or UTP and none by ADP. These results indicate that the Ca2+ -ATPase described in this paper is the enzyme which drives active transport of Ca2+ at the plasma membrane of higher plants