Interaction between alkali light chains of myosin and divalent metal ions.

1. Difference UV absorption spectra of chicken breast g1 induced by magnesium and calcium ions were compared with those of rabbit skeletal alkali light chains. The value of delta epsilon due to the burial of Tyr 180 of domain 4 was about one-fourth of that of rabbit alkali light chains. Regions other than domain 4 appear to affect the environment of Tyr 180, since the first-order structure of domain 4 of chicken g1 is present in rabbit g1 without significant alteration (Matsuda, G. et al. (1981) FEBS Lett. 126, 111). Movement of a phenylalanyl residue was suggested to be larger in chicken g1 than rabbit g1. 2. CD spectra of alkali light chains were measured in the wavelength region down from 260 nm. Divalent metal ions increased the helix content of alkali light chains about 2%. CB1 peptide of rabbit skeletal g1 containing domain 1 showed a slight change of CD spectrum in the presence of divalent ions. These results suggest that domain 1 of alkali light chains binds divalent ions. 3. Binding of calcium ions to rabbit skeletal g1 was directly measured by means of a calcium ion selectrode. More than 3 mol of calcium was bound per mol of g1. The concentration of free calcium ions required to give a half-maximal binding was 5 mM assuming that the maximum binding number is 4 mol of calcium per mol of g1. 4. Nitration of tyrosyl residues in rabbit skeletal g1 may slightly affect the affinity for divalent metal ions and the backbone structure of the polypeptide chain of g1.