Purification and Properties of the Components from Troponin

Procedures have been developed for purification of three of the four protein components usually found in skeletal muscle troponin preparations. These three components are the ones required for troponin activity, and an apparent functional property of each has been defined. TN-I with a molecular weight of 24,000 inhibits actomyosin ATPase activity both in the presence and absence of Ca++. TN-T, with a molecular weight of 37,000, interacts with tropomyosin as evidenced by the appearance of a new hypersharp peak when mixtures of the two proteins are examined in the analytical ultracentrifuge. TN-C, with a molecular weight of 20,000, was the only component which possesses high affinity Ca++ binding activity. The sulfhydryl groups of troponin are found only in TN-I and TN-C. TN-I and TN-T require salt for full solubility and both proteins show a strong tendency to aggregate. An attempt has been made to interpret results on troponin fractionation obtained in other laboratories in the light of the properties of our purified components.