Sulfhydryl Groups of the “Relaxing Protein” from Rabbit Skeletal Muscle*

Abstract

The sedimentation pattern of usual preparations of the relaxing protein is a single, sharp peak, but we found a few preparations to have two peaks. Metal-chelators or sulfhydryl compounds made the two peaks into a single peak whose s₂₀ w (2.7 mg per ml, μ∼0.22) was exactly the same as that of the single-peak preparation (5.1S). The relaxing protein prepared in the presence of ethylene glycol-bis (β-aminoethylether)-N, N'-tetraacetic acid contained 4.9 moles of sulfhydryl groups (SH) per 10⁵ g. When incubated with N-ethylmaleimide, the SH content of the relaxing protein was reduced to 1.3 moles per 10⁵ g, whereas the relaxing activity of the protein was affected very little.