Incubation of Myosin with Exogenous Small Components (g1, g2, or g3) in KSCN or LiCl and Properties of g-Exchanged Myosins1

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Abstract
Myosin was incubated with a large excess of exogenous g1, g2, or g3, in 0.6 M KSCN (or in 4 M LiCl) for 1–2 h at 0–2°C. KSCN (or LiCl) was then removed by dialysis. The composition of g-chains in the resulting myosin was analyzed by SDS-gel electrophoresis. When myosin was incubated with g1 the amount of g1 in myosin increased and the increment was nearly counterbalanced by a decrease in g3, whereas an opposite change was observed on incubation with g3. The amount of g2 was not changed by these treatments. The same ATPase activity as that of control myosin was observed in the presence of Ca2+ or EDTA with the myosins incubated with g1, g2, or g3, but the activity in the presence of Mg2+ was about one-half of the control. The Ca2+ sensitivity of actomyosin containing the treated myosins was slightly higher than that of actomyosin containing the control myosin. Spin-labeled g1 or spin-labeled g3 was incorporated into myosin, but the ESR spectra of two spin labels were not distinguishable. No information could be obtained from the ESR spectra by the addition of Ca2+, Mg2+, nucleotides or actin. Inhibition of ATPase activity was observed when SH groups of g1 or g3 in myosin were chemically modified.