We studied the effects of the troponin components TN-T, TN-I and TN-C, and of Ca2+ concentration on the dissociation temperature of the F-actin · tropomyosin complex. Troponin components and their complexes increased the dissociation temperature in the following sequence of effectiveness: TN-C(±Ca2+) < TN-I < TN-I · TN-C(±Ca2+) ≪ TN-T · TN-C(+Ca2+) ≪ TN-T · TN-C(-Ca2+) ≈ TN-T < TN-T · TN-I · TN-C(+Ca2+) < TN-T · TN-I · TN-C-(-Ca2+) ≈ TN-T · TN-I; TN-C has no effect. The effect of TN-I is small. TN-T is the most important component for increasing the dissociation temperature. The shifting by Ca2+ of the dissociation temperature to lower values is only seen when both TN-T and TN-C are present.
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