Fractionation of troponin into two distinct proteins

The protein complex which governs the calcium sensitivity of natural actomyosin (Ebashi, 1963) has been shown to consist of two components, tropomyosin and troponin (Ebashi and Kodama, 1966; Hartshorne and Mueller, 1967). In the present study troponin has been separated into two distinct proteins, as judged by amino acid analyses. The fractionation was achieved at low pH and high ionic strength. One of the fractions, termed troponin B, effected a calcium insensitive inhibition of synthetic actomyosin ATPase activity, which was enhanced by the addition of tropomyosin. The other fraction, troponin A, conferred calcium sensitivity to the troponin B - tropomyosin system. The separation was reversible and all the properties of the source troponin were regained upon mixing troponin A and B in the correct proportions.