Limited tryptic modification stimulates activation of Ca2+ release from isolated sarcoplasmic reticulum vesicles.

Trimm, Jonathan L.; Salama, Guy; Abramson, Jonathan J.

doi:10.1016/s0021-9258(19)77856-9

Cited by 11 publications

(1 citation statement)

References 34 publications

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“…The 170000-Da protein reacts with Stains-all as a glycoprotein, binds doxorubicin (Zorzato & Volpe, 1988), and has been suggested to be the caffeine receptor of the SR Ca2+ release channel (Rubstov & Murphy, 1988). It should be pointed out that the 450000-Da channel protein is highly susceptible to proteolysis (Seiler et al, 1984;Chu et al, 1988b;Lai et al, 1988;Trimm et al, 1988;Meissner et al, 1989) and the 170000-Da band may contain such a derived frag- alter the kinetics of Ca2+-and nucleotide-induced Ca2+ release from JTC. Ca2+ release was measured after loading JTC with 1 mM ATP for 2 min as described above, in the absence (closed symbols) or in…”

Section: Time Secondsmentioning

confidence: 99%

Specific association of calmodulin-dependent protein kinase and related substrates with the junctional sarcoplasmic reticulum of skeletal muscle

Chu

Sumbilla²,

Inesi³

et al. 1990

Biochemistry

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A systematic study of protein kinase activity and phosphorylation of membrane proteins by ATP was carried out with vesicular fragments of longitudinal tubules (light SR) and junctional terminal cisternae (JTC) derived from skeletal muscle sarcoplasmic reticulum (SR). Following incubation of JTC with ATP, a 170,000-Da glycoprotein, a 97,500-Da protein (glycogen phosphorylase), and a 55,000-60,000-Da doublet (containing calmodulin-dependent protein kinase subunit) underwent phosphorylation. Addition of calmodulin in the presence of Ca2+ (with no added protein kinase) produced a 10-fold increase of phosphorylation involving numerous JTC proteins, including the large (approximately 450,000 Da) ryanodine receptor protein. Calmodulin-dependent phosphorylation of the ryanodine receptor protein was unambiguously demonstrated by Western blot analysis. The specificity of these findings was demonstrated by much lower levels of calmodulin-dependent phosphorylation in light SR as compared to JTC, and by much lower cyclic AMP dependent kinase activity in both JTC and light SR. These observations indicate that the purified JTC contain membrane-bound calmodulin-dependent protein kinase that undergoes autophosphorylation and catalyzes phosphorylation of various membrane proteins. Protein dephosphorylation was very slow in the absence of added phosphatases, but was accelerated by the addition of phosphatase 1 and 2A (catalytic subunit) in the absence of Ca2+, and calcineurin in the presence of Ca2+. Therefore, in the muscle fiber, dephosphorylation of SR proteins relies on cytoplasmic phosphatases. No significant effect of protein phosphorylation was detected on the Ca2(+)-induced Ca2+ release exhibited by isolated JTC vesicles. However, the selective and prominent association of calmodulin-dependent protein kinase and related substrates with junctional membranes, its Ca2+ sensitivity, and its close proximity to the ryanodine and dihydropyridine receptor Ca2+ channels suggest that this phosphorylation system is involved in regulation of functions linked to these structures.

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