STUDIES ON TROPONIN

Troponin was isolated from preparations of the ethylene glycol bis-(β-aminoethyl ether)-N,N′-tetraacetic acid (EGTA)-sensitizing factor over the pH range of 3.5-4.6. The variations among troponins were due essentially to differences in the proportion and properties of the troponin A component. This was dictated by the choice of the source fraction (EGTA-sensitizing factor) and by the efficiency of recovery of troponin A in troponin by the isoelectric fractionation. A higher yield of troponin A was obtained at the alkaline edge of the given pH range. The relative proportion of troponin A in troponin was reflected by the A278 mμ:A260 mμ ratio and by the effect troponin had on the Mg2+-activated ATPase activity of synthetic actomyosin. The inhibitory effect of the EGTA-sensitizing factor on the Mg2+-activated ATPase activity of synthetic actomyosin in the presence of EGTA, was due to an interaction of troponin B and tropomyosin. Ultracentrifugal analysis revealed that this interaction was reflected by the formation of a hypersharp boundary different from the boundaries of troponin B or tropomyosin alone. Inhibition of the ATPase activity and complex formation was maximal at a ratio of tropomyosin to troponin B of approx. 1:1 (w/w). It is proposed that troponin A is responsible for the calcium sensitivity of the EGTA-sensitizing factor. © 1969.