Key result
Tropomyosin binds F-actin at a 1:2 weight ratio and modifies actin polymerization properties.
Why the study?
The interaction of tropomyosin with F-actin under various conditions and its localization in thin filaments was not fully characterized.
Findings remain preclinical; extends in vitro mapping of tropomyosin-F-actin stoichiometry but leaves in vivo relevance open.
The interaction of tropomyosin with F‐actin was studied under various conditions. The maximum ratio of tropomyosin bound to actin was found by ultracentrifugation to be 1:2, by weight. Viscometric study showed, however, no further increase of viscosity due to formation of the actin‐tropomyosin complex when the above ratio exceeded 1:5. Higher ionic strength caused dissociation of the complex. The comparison of the rate of polymerization of tropomyosin free actin under various salt conditions with that in the presence of tropomyosin showed that the latter partially modified some properties of actin. The pattern of polymerization of actin extracted at room temperature (RT‐actin) resembled that of the mixtures of actin with tropomyosin, although some differences were observed indicating tighter binding in the case of RT‐actin, possibly due to the presence of troponin. The results obtained are discussed from the point of view of the possible localization of tropomyosin in thin flaments.
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Drabikowski et al. (1968) studied this question. Tropomyosin vs. Tropomyosin-free actin was evaluated on Maximum ratio of tropomyosin bound to actin and polymerization properties. The maximum ratio of tropomyosin bound to F-actin was 1:2 by weight, with higher ionic strength causing complex dissociation and tropomyosin partially modifying actin polymerization properties.
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