Abstract
Troponin prepared from rabbit skeletal muscle in the presence of dithiothreitol (SH-troponin) was found to have a sulfhydryl content of about 4 moles 1 × 10 5 g in the presence of a Ca 2+-chelating agent. The addition of physiological concentrations of Ca 2+ reduced the reactive sulfhydryl content to 2.0–2.5 moles 1 × 10 5 g . These sulfhydryl groups are evidently not direct participants in the inhibition of actomyosin superprecipitation, since treatment with N-ethylmaleimide had no effect on the Ca 2+-sensitizing activity of SH-troponin. Troponin prepared in the absence of dithiothreitol (S-S-troponin) showed a significant reduction in Ca 2+-sensitizing activity, relative to SH-troponin. The sulfhydryl groups of S-S-troponin, approx. 2 moles 1 × 10 5 g were not appreciably affected by Ca 2+. It is postulated that the Ca 2+-sensitive sulfhydryl groups exist at a site which is essential for the regulatory function of troponin and which undergoes a conformational change upon the binding of Ca 2+.
Published Version
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