Effect of calcium and F-actin on the rate of SH2 modification in skeletal myosin |
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Authors: | Tsuneo Kameyama Mitsuko K. Ishii Takashi Yoshiike |
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Affiliation: | (1) Department of Biochemistry, School of Medicine, Juntendo University, Hongo-2, Bunkyo-ku, 113 Tokyo, Japan;(2) Department of Dermatology, School of Medicine, Juntendo University, Hongo-2, Bunkyo-ku, 113 Tokyo, Japan |
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Abstract: | The rate constant of modification of a specific thiol group, SH2, with N-ethylmaleimide (NEM) has been used to estimate the conformational change in the local area containing SH2 (SH2 region) of skeletal myosin as a structural probe. The rate of Mg2+-ATP-induced SH2 modification of subfragment-1 (S-l) isozymes was regulated by Ca2+ in the pCa range below 6.4 and was not regulated in the pCa range above 6.4. No substantial difference between S-1 containing alkali light chain, A1, (S-1(A1)) and S-1 containing alkali light chain, A2, (S-1(A2)) was observed in the Ca2+-dependent rate of SH2 modification. Due to the presence of this Ca2+ regulation in myosin (absence in S-1 isozymes) in the pCa range above 6.4, absence of 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) light chain in S-1 isozymes, and high affinity of Ca2+ for DTNB light chain, this Ca2+ regulation in the pCa range above 6.4 is possibly related to the Ca2+ binding to DTNB light chain. F-Actin, which is entirely free from tropomyosin and troponin, enhanced the rate of Mg2+-ATP-induced SH2 modification of S-1 isozymes equally and of myosin, and reduced the Ca2+ sensitivity with an increase in F-actin concentration. |
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Keywords: | calcium F-actin myosin SH2 region |
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