PT - JOURNAL ARTICLE AU - Yutaka Hirata AU - Norimichi Nakahata AU - Yasushi Ohizumi TI - Identification of a 97-kDa Mastoparan-Binding Protein Involving in Ca<sup>2+</sup> Release from Skeletal Muscle Sarcoplasmic Reticulum DP - 2000 Jun 01 TA - Molecular Pharmacology PG - 1235--1242 VI - 57 IP - 6 4099 - http://molpharm.aspetjournals.org/content/57/6/1235.short 4100 - http://molpharm.aspetjournals.org/content/57/6/1235.full SO - Mol Pharmacol2000 Jun 01; 57 AB - Mastoparan (MP) and radiolabeled [Tyr3]MP caused a transient Ca2+ release from the heavy fraction of sarcoplasmic reticulum, which was inhibited by ryanodine. MP enhanced [3H]ryanodine binding in a concentration-dependent manner with an EC50 value of approximately 0.3 μM. The45Ca2+ release was accelerated by MP, [Tyr3]MP, or caffeine in a concentration-dependent manner. The EC50 values for MP, [Tyr3]MP, and caffeine were approximately 2.0 μM, 7.7 μM, and 1.8 mM, respectively. MP, like caffeine, shifted the stimulatory limb of a bell-shaped curve of Ca2+ dependence to the left.45Ca2+ release induced by caffeine was completely inhibited by typical blockers of Ca2+-induced Ca2+ release, such as Mg2+, ruthenium red, or procaine. However, 45Ca2+ release induced by MP was completely inhibited by Mg2+, but it was only partially inhibited by ruthenium red or procaine. The rate of45Ca2+ release induced by MP was further increased in the presence of caffeine, showing that the MP binding site is different from that of caffeine on Ca2+ release channels. We succeeded in the synthesis of125I-[Tyr3]MP with a high specific activity.125I-[Tyr3]MP bound specifically to heavy fraction of sarcoplasmic reticulum with a Kdvalue of 4.0 μM and a Bmax value of 3.0 nmol/mg. Furthermore, 125I-[Tyr3]MP specifically cross-linked to the 97-kDa protein without direct binding to ryanodine receptor. The protein was not triadin or Ca2+-pump, because antitriadin antibody and anti-Ca2+-pump antibody did not immunoprecipitate the protein. These results suggest that the 97-kDa MP-binding protein may have an important role in the excitation-contraction coupling of skeletal muscle. The American Society for Pharmacology and Experimental Therapeutics