Open AccessBasal Mg 2+ ‐dependent ATPase activity of rat liver microsomes is not influenced by ambient free Ca 2+
Author(s) -
PUT Frans H. M. M.,
VISSER Gea J.,
DONKERS Elizabeth A. M.,
THEUVENET Alexander P. R.,
WILLEMS Peter H. G. M.
Publication year - 1993
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1993.tb18453.x
Subject(s) - thapsigargin , atpase , microsome , chemistry , basal (medicine) , calcium , endocrinology , medicine , calcium atpase , enzyme assay , enzyme , biochemistry , biophysics , endoplasmic reticulum , biology , organic chemistry , insulin
The potent inhibitor of Ca 2+ , Mg 2+ ‐ATPase activity, thapsigargin, has been used to investigate the effect of ambient free Ca 2+ on basal Mg 2+ ‐dependent ATPase activity in rat liver microsomes. Thapsigargin non‐competitively inhibited both Ca 2+ ‐stimulated ATP‐dependent Ca 2+ uptake and Ca 2+ ‐stimulated Mg 2+ ‐dependent ATPase activity. At a concentration of 1 μM, thapsigargin completely inhibited the Ca 2+ ‐pump activity, without affecting Mg 2+ ‐dependent ATPase activity measured in the absence of Ca 2+ . Increasing the ambient free Ca 2+ concentration did not alter the basal Mg 2+ ‐dependent ATPase activity. The data presented indicate that ATPase activity measured in the absence of Ca 2+ is a reliable measure for the basal Mg 2+ ‐dependent ATPase activity and that, consequently, the Ca 2+ ‐stimulated Mg 2+ ‐dependent ATPase activity can indeed be defined as the difference between the ATPase activity measured in the presence and the absence of Ca 2+ .