Conformational changes of the in situ red cell membrane calcium pump affect its proteolysis

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In inside-out red cell membrane vesicles trypsin digestion reduces the molecular mass of the 32P-labeled acyl-phosphate intermediate of the calcium pump from the original 140 kDa to about 80 kDa with a simultaneous activation of the calcium uptake. This process is slightly stimulated by the presence of calcium, as compared to EGTA, or EGTA + vanadate, but the proteolytic pattern is similar under all these conditions. However, trypsin degradation of the 80 kDa polypeptide, resulting in the loss of calcium transport activity and 32P-phosphoenzyme formation, is rapid in the presence of calcium, inhibited by EGTA and almost fully blocked by EGTA + vanadate. In the presence of these latter ligands, probably locking the calcium pump in an E2 conformation, the 80 kDa protein becomes insensitive even to excessive digestion by the non-specific protease, pronase. The data indicate major changes in the molecular arrangement of the calcium pump protein when transformed from a calcium-liganded (E1) to an E2 conformation.

Original languageEnglish
Pages (from-to)129-133
Number of pages5
JournalBBA - Biomembranes
Issue number1
Publication statusPublished - May 12 1987


  • (Red cell membrane)
  • Calcium pump
  • Conformational change
  • Inside-out vesicle
  • Phosphorylation
  • Proteolysis
  • Vanadate

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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