Molecular properties of the red cell calcium pump: I. Effects of calmodulin, proteolytic digestion and drugs on the kinetics of active calcium uptake in inside-out red cell membrane vesicles

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Abstract

In calmodulin-stripped inside-out human red cell membrane vesicles /IOV/ ATP + Mg2+-dependent active calcium uptake is stimulated by the addition of calmodulin. Calmodulin increases the maximum calcium transport rate /Vmax/, decreases KCa, and does not affect KATP of calcium uptake. The action of both membrane bound and external calmodulin is competitively inhibited by phenothiazines. Drugs reacting with SH groups of proteins reversibly inhibit calcium pumping by decreasing Vmax and not affecting KCa and KATP. The relative magnitude of calmodulin stimulation of calcium transport is unaltered by SH reagents. Mild proteolytic digestion of IOVs stimulates active calcium uptake and mimics the effects of calmodulin on the kinetic parameters — that is converts the system to a “high calcium-affinity” state. Proteolysis eliminates calcium-dependent calmodulin binding to IOV membranes and any further stimulation of calcium uptake by calmodulin. Based on these results the presence of a calmodulin-binding regulatory subunit of the red cell calcium pump at the internal membrane surface is postulated.

Original languageEnglish
Pages (from-to)287-297
Number of pages11
JournalCell Calcium
Volume1
Issue number5
DOIs
Publication statusPublished - jan. 1 1980

ASJC Scopus subject areas

  • Physiology
  • Molecular Biology
  • Cell Biology

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