Active Uptake of Ca++ and Ca++-Activated Mg++ ATPase in Red Cell Membrane Fragments

Abstract

Isolated human red blood cell membrane fragments (RBCMF) were found to take up Ca++ in the presence of ATP.

Phosphorylation of the red blood cell membrane during the active transport of C++.

“…If this is the case, then the different results obtained in their and the present study may be reconciled by assuming that Ca ++ is required for the step from E1-P to Ez-P. Since the Ca ++ transport ATPase is very sensitive to temperature and no dephosphorylation occurs at 0°C (Cha et al, 1971), the presence of Ca ++ would increase phosphorylation by forming E2-P without dephosphorylation of this intermediate at 0°C in the study of Knauf et al (1974 b). As discussed by the authors in their study, another cause of increased phosphorylation by Ca ++ was the inhibition of dephosphorylation of Na+-K+-ATPase by Ca ++.…”

“…Previously, it was found that when red blood cells are fragmented, red blood cell membrane fragments (RBCMF) were found to take up Ca ++ and this Ca ++ uptake is accompanied by ATP hydrolysis by Mg++-activated ATPase (Lee and Shin, 1969;Cha et al 1971). It has been suggested that this Ca ++ uptake is due to the presence of inside out vesicles in the present system although not all of the vesicles are inside out (Steck et al, 1970;Weiner and Lee, 1972).…”

“…RBCMF were prepared according to the procedure used previously in this laboratory (Cha et al, 1971).…”

“…The Ca ++ uptake of RBCMF was measured according to the method of Cha et al (1971) employing 4"~Ca. In this method, the radioactivity of RBCMF after incubation of RBCMF with 4"~Ca in the presence of ATP was measured.…”

“…It has been shown previously that the red blood cell membrane has an active transport mechanism for outward extrusion of Ca ++ (Schatzmann and Vincenzi, 1969;Lee and Shin, 1969), and ATP is the specific energy source of the Ca ++ transport system (Vincenzi and Schatzmann, 1967;Cha et al, 1971).…”