Salt-induced conformational changes in skeletal myosin light chains, troponin-C, and parvalbumin

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Abstract
Evidence for salt-induced changes in myosin L chains [dissociated by treatment with 5,5''-dithiobis(2-nitrobenzoic acid) (DTNB)], troponin-C (TnC) and parvalbumin was obtained from chymotryptic digestion, circular dichroism, fluorescence and difference absorption studies. High salt (0.6 M NaCl) protects the DTNB L chain from proteolysis, increases its .alpha.-helical content, and quenches the tryptophan fluorescence. These effects are similar to the changes induced by Ca2+ but smaller in magnitude. TnC is affected by monovalent cations in a similar manner. Changes in the .alpha.-helical content resemble the effect of Ca2+. The enhancement of tyrosine fluorescence reflects conformational changes in the Ca2+-Mg2+ binding sites. The increase in the fluorescence of dansylaziridine-labeled TnC suggests perturbation of Ca2+-specific sites by salt. Cancellation of this effect by Mg2+ binding to the high-affinity sites is indicative of site-site interactions. In Whiting parvalbumin, salt induced a perturbation of tryptophan absorption similar in nature to the Ca2+ effect.