Trypsin digestion of junctional sarcoplasmic reticulum vesicles

Biochemistry. 1988 Apr 19;27(8):2827-33. doi: 10.1021/bi00408a025.


A putative constituent of the junctional processes, connecting the terminal cisternae of sarcoplasmic reticulum and the transverse tubules of skeletal muscle fibers, is a greater than or equal to 350,000-dalton (Da) protein that displays ryanodine binding and Ca2+ channel properties. Ryanodine modulation of Ca2+ fluxes suggests that the ryanodine receptor and calcium channel are integral parts of one functional unit corresponding to the greater than or equal to 350,000-Da protein [Inui, M., Saito, E., & Fleischer, S. (1987) J. Biol. Chem. 262, 1740-1747; Campbell, K. P., Knudson, C. M., Imagawa, T., Leung, A. L., Sutko, J. L., Kahl, S. D., Raab, C. R., & Madson, L. (1987) J. Biol. Chem. 262, 6460-6463]. We subjected vesicular fragments of junctional-cisternal membrane to stepwise trypsin digestion. The greater than or equal to 350,000-Da protein is selectively cleaved in the early stage of digestion, with consequent disappearance of the corresponding band in electrophoretic gels. The Ca2+-ATPase is cleaved at a later stage, while calsequestrin is not digested under the same experimental conditions. While the Ca2+-ATPase yields two complementary fragments that are relatively resistant to further digestion, the greater than or equal to 350,000-Da protein yields fragments that are rapidly broken down to small peptides. Under conditions producing extensive digestion of the greater than or equal to 350,000-Da protein, the junctional processes are still visualized by electron microscopy, with no discernible alterations of their ultrastructure. The functional properties of the Ca2+ release channel are also maintained following trypsin digestion, including blockage by Mg2+ and ruthenium red and activation by Ca2+ and nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium-Transporting ATPases / metabolism
  • Kinetics
  • Microscopy, Electron
  • Molecular Weight
  • Muscle Proteins / isolation & purification
  • Muscle Proteins / metabolism*
  • Muscles / metabolism
  • Muscles / ultrastructure
  • Rabbits
  • Ryanodine / metabolism
  • Sarcoplasmic Reticulum / ultrastructure*
  • Trypsin*


  • Muscle Proteins
  • Ryanodine
  • Trypsin
  • Calcium-Transporting ATPases
  • Calcium