Abstract
Calpain treatment of rabbit skinned muscle fibers resulted in proteolysis of junctional foot protein or Ca 2+ release channel of the sarcoplasmic reticulum. Electrophoretic and immunoblot analyses indicate that calpain cleaves off ∼130 kDa peptide from the N-terminus. After such treatment, Ca 2+ capacity of the sarcoplasmic reticulum remained normal and both Ca 2+ and adenine nucleotide dependence of Ca 2+-induced Ca 2+ release mechanism were retained. However, the Ca 2+-activated Ca 2+ release rate was increased by two fold after the proteolysis. The results suggest the presence of functional domains in the junctional foot protein, and the N-terminus domain controls the activity of the Ca 2+ channel without changing Ca 2+ and nucleotide sensitivities.
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