Carp troponin was extracted with 0.4M LiCI from washed muscle and purified by SP-Sephadex chromatography. The purified troponin showed three components, with molecular weights of 30, 000 21, 000, and 19, 000, on its SDS-polyacrylamide gel electrophoretogram.
The troponin was fractionated into its 19, 000 component and a complex of its 30, 000 and 21, 000 components by chromatography on SP-Sephadex in 6M urea (pH 6.4) with a linear KCI gradient. The 30, 000 component and a complex of 19, 000 and 21, 000 components were separated from the troponin by SP-Sephadex chromatography in an alkaline solution containing 6M urea. The 21, 000 component was isolated from the complex of 19, 000 and 21, 000 components by DEAE-Sephadex chromatography in 6M urea.
The 19, 000 component is a water soluble protein and has a characteristic ultraviolet absorption spectrum with maxima at 253, 259, 265, 269, 275, and 283 nm. The 30, 000 component is a water insoluble protein.
In the absence of tropomyosin, neither the 19, 000 component, the complex of 30, 000 and 21, 000 components, nor a mixture of these three components had any effect on the calcium sensitivity of desensitized carp actomyosin. In the presence of tropomyosin, neither the 19, 000 component, the 30, 000 component, nor the mixture of both components had any effect on the ATPase activity of the desensitized actomyosin. Both the complex of 30, 000 and 21, 000 components and the complex of 19, 000 and 21, 000 components inhibited the ATPase activity in both the presence and the absence of Ca
2+. The 19, 000 component effectively neutralized the inhibitory effect of the complex of 30, 000 and 21, 000 components only in the presence of Ca
2+. The troponin activity was completely reproduced when all three components were added to the desensitized actomyosin in the presence of tropomyosin.
The 30, 000, 21, 000, and 19, 000 components of carp troponin were identified as troponin-T, -I, and -C, respectively, on the basis of these results.
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