Key result
Binding of muscle tropomyosin to muscle F-actin at an 8.4/1.0 molar ratio protects 58% of the F-actin from depolymerization by actin-depolymerizing factor for at least 3 hours.
Why the study?
Does tropomyosin binding to F-actin protect it from depolymerization by actin-depolymerizing factor in vitro?
Does tropomyosin binding to F-actin protect it from depolymerization by actin-depolymerizing factor in vitro?
Tropomyosin binding specifically protects F-actin filaments from disassembly by actin-depolymerizing factor in vitro.
May inform cytoskeletal regulation models; leaves open in vivo relevance for cell motility.
Brain or muscle F-actin is rapidly depolymerized to monomeric actin in vitro by actin-depolymerizing factor, a protein isolated from chick embryo brain. Binding of muscle tropomyosin to muscle F-actin protects the F-actin from depolymerization by this factor. A 8.4/1.0 molar ratio of actin subunits to tropomyosin, achieved by incubation of the F-actin with excess tropomyosin, protects 58% of the F-actin from depolymerization by excess actin-depolymerizing factor for at least 3 hr at 25 degrees C. Thus, actin-depolymerizing factor seems to be specifically directed toward actin filaments lacking tropomyosin.
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Bernstein et al. (1982) studied this question. Tropomyosin binding to F-actin vs. F-actin lacking tropomyosin was evaluated on Protection from depolymerization by excess actin-depolymerizing factor. Binding of muscle tropomyosin to muscle F-actin at an 8.4/1.0 molar ratio protects 58% of the F-actin from depolymerization by actin-depolymerizing factor for at least 3 hours.
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