Kinetic characterization of calcium uptake by the rat liver Golgi apparatus.

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 μm thapsigargin but not stimulated by 3 μm calmodulin. The kinetic parameter values obtained for the GA Ca2+pump were: Jmaxof 3.96 nmol/mg min, Kmfor Ca2+of 0.150 μm and two Km's for ATP of 1.14 μm and 519 μm. 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.