Tryptic digestion of sarcoplasmic reticulum inhibits Ca2+ accumulation by action on a membrane component other than the Ca2+-ATPase.

V. Shoshan-Barmatz, N. Ouziel, D. M. Chipman

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

We have reexamined the "uncoupling" of Ca2+ transport from ATP hydrolysis, which has been reported to be caused by trypsin cleavage of the Ca2+-ATPase of sarcoplasmic reticulum (SR) vesicles at the second (slower) of two characteristic tryptic sites (Scott, T. L., and Shamoo, A. E. (1982) J. Membr. Biol. 64, 137-144). We find that the loss of Ca2+ accumulation capacity in SR vesicles is poorly correlated with this cleavage under several conditions. The loss is accompanied by increased Ca2+ permeability but not by changes in the properties of the ATPase or ATP-Pi exchange activities of the vesicles. Proteoliposomes containing purified Ca2+-ATPase which has been cleaved in part at the two tryptic sites are as well coupled and impermeable to Ca2+ as proteoliposomes containing intact Ca2+-ATPase. We conclude that the loss of Ca2+ accumulation capacity in SR vesicles on tryptic treatment is due to cleavage of a SR membrane component other than the Ca2+-ATPase, possibly a component of the gated channels which function in Ca2+ release from SR, which leads to a Ca2+ leak. The hydrolytic and coupled transport functions of the Ca2+-ATPase itself may well be unaffected by the two tryptic cleavages.

Original languageEnglish
Pages (from-to)11559-11564
Number of pages6
JournalJournal of Biological Chemistry
Volume262
Issue number24
StatePublished - 25 Aug 1987

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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