Further characterization of the red beet plasma membrane Ca2+-ATPase using GTP as an alternative substrate

Lorraine E. Williams, Sherry B. Schueler, Donald P. Briskin

Research output: Contribution to journalArticlepeer-review


The GTP-driven component of Ca2+ uptake in red beet (Beta vulgaris L) plasma membrane vesicles was further characterized to confirm its association with the plasma membrane Ca2+-translocating ATPase and assess its utility as a probe for this transport system. Uptake of 45Ca2+ in the presence of GTP demonstrated similar properties to those previously observed for red beet plasma membrane vesicles utilizing ATP with respect to pH optimum, sensitivity to orthovanadate, dependence on Mg:substrate concentration and dependence on Ca2+ concentration. Calcium uptake in the presence of GTP was also strongly inhibited by erythrosin B, a potent inhibitor of the plant plasma membrane Ca2+-ATPase. Furthermore, after treatment with EGTA to remove endogenous calmodulin, the stimulation of 45Ca2+-uptake by exogenous calmodulin was nearly equivalent in the presence of either ATP or GTP. Taken together these results support the proposal that GTP-driven 45Ca2+ uptake represents the capacity of the plasma membrane Ca2+-translocating ATPase to utilize this nucleoside triphosphate as an alternative substrate. When plasma membrane vesicles were phosphorylated with [γ-32P]-GTP, a rapidly turning over, 100 kilodalton phosphorylated peptide was observed which contained an acyl-phosphate linkage. While it is proposed that this peptide could represent the catalytic subunit of the plasma membrane Ca2+-ATPase, it is noted that this molecular weight is considerably lower than the 140 kilodalton size generally observed for plasma membrane Ca2+-ATPases present in animal cells.

Original languageEnglish (US)
Pages (from-to)747-754
Number of pages8
JournalPlant physiology
Issue number3
StatePublished - Mar 1990
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science


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