Tropomyosin inhibits the rate of actin polymerization by stabilizing actin filaments

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Abstract
Tropomyosin inhibition of the rate of spontaneous polymerization of actin is associated with binding of tropomyosin to actin filaments. Rate constants determined by using a direct electron microscopic assay of elongation showed that .alpha..alpha.- and .alpha..beta.-tropomyosin have a small or no effect on the rate of elongation at either end of the filaments. The most likely explanation for the inhibition of the rate of polymerization of actin in bulk samples is that tropomyosin reduces the number of filaments ends by mechanical stabilization of the filaments.