title: Effect of calcium and F-actin on the rate of SH2 modification in skeletal myosin.
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-1) 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.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D009132:Muscles / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D000199:Actins; D013438:Sulfhydryl Compounds; D000255:Adenosine Triphosphate; D009218:Myosins; D000252:Calcium-Transporting ATPases; D005033:Ethylmaleimide; D002118:Calcium