Ca(2+) sequestering in the early-branching amitochondriate protozoan Tritrichomonas foetus: an important role of the Golgi complex and its Ca(2+)-ATPase.
Total membrane vesicles isolated from Tritrichomonas foetus showed an ATP-dependent Ca(2+) uptake, which was not sensitive to 10 microM protonophore FCCP but was blocked by orthovanadate, the inhibitor of P-type ATPases (I(50)=130 microM), and by the Ca(2+)/H(+) exchanger, A-23187. The Ca(2+) uptake was prevented also by thapsigargin, an inhibitor of the SERCA Ca(2+)-ATPases. The sensitivity of the Ca(2+) uptake by the protozoan membrane vesicles to thapsigargin was similar to that of Ca(2+)-ATPase from rabbit muscle sarcoplasmic reticulum. Fractionation of the total membrane vesicles in sucrose density gradient revealed a considerable peak of Ca(2+) transport activity that co-migrated with the Golgi marker guanosine diphosphatase (GDPase). Electron microscopy confirmed that membrane fractions of the peak were enriched with the Golgi membranes. The Golgi Ca(2+)-ATPase contributed to the Ca(2+) uptake by all membrane vesicles 80-85%. We conclude that: (i) the Golgi and/or Golgi-like vesicles form the main Ca(2+) store compartment in T. foetus; (ii) Ca(2+) ATPase is responsible for the Ca(2+) sequestering in this protozoan, while Ca(2+)/H(+) antiporter is not involved in the process; (iii) the Golgi pump of this ancient eukaryotic microorganism appears to be similar to the enzymes of the SERCA family by its sensitivity to thapsigargin.
Almeida
João C A
JC
Laboratório de Fisiologia e Bioqui;mica de Microorganismos, Centro de Biociencias e Biotechnol., Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ 28013-600, Brasil.
Benchimol
Marlene
M
de Souza
Wanderley
W
Okorokov
Lev A
LA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D016835:Tritrichomonas foetus / Q000378:metabolism* / Q000648:ultrastructure
D000252:Calcium-Transporting ATPases; D002118:Calcium