Abstract

We carried out a kinetic characterization of the Ca2+ active transport in the rat liver Golgi Apparatus (GA) membrane. Calcium accumulation by vesicles of a GA enriched fraction was found to be a function of both Ca2+ and ATP-Mg concentrations, it was inhibited by 2 muM thapsigargin but not stimulated by 3 muM calmodulin. The kinetic parameter values obtained for the GA Ca2+ pump were: J(max) of 3.96 nmol/mg min, K-m for Ca2+ of 0.150 muM and two K-m's for ATP of 1.14 muM and 519 muM. These results were almost identical to those obtained for the endoplasmic reticulum (ER) fraction, indicating that the GA Ca2+ pump is a sarco/endoplasmic reticulum (SERCA) P-type, analogous-if not identical-to that present in the ER. (C) 2000 Academic Press.