Wikman-Coffelt, J., Higuchi, M., Fábián, F. & Mason, D. T.

Comparison of Mg2+ vs Ca2+, K+ and actin-activation of myosin after trinitrophenylation.

Res Commun Chem Pathol Pharmacol 25, 565-75.

While modification of six lysyl residues causes a near maximal decrease in Ca2+, K+, and actin + Mg2+ -activated myosin ATPase activities in rabbit skeletal muscle myosin, it takes nearly twice this number of modified lysyl groups to cause a similar alteration in canine cardiac myosin where trinitrophenylation is nonspecific. It appears that there are several rapidly reacting lysyl residues in cardiac myosin; the active site of cardiac myosin is protected by ATP after modification of a limited number of these rapidly reacting lysyl groups. In both myosins, after a charge modification of these rapidly reacting lysyl groups, 6 in rabbit skeletal muscle myosin and 10 in canine cardiac myosin, there is a decrease in Ca2+, K+, and actin + Mg2+ -stimulation of myosin but an activation of Mg2+ -stimulated myosin ATPase activity, thus making actin + Mg2+ -stimulated myosin ATPase activity more like activation with K+ or Ca2+ as compared to activation with Mg2+ alone.

Szilágyi, L., Bálint, M., Sreter, F. A. & Gergely, J.

Photoaffinity labelling with an ATP analog of the N-terminal peptide of myosin.

Biochem Biophys Res Commun 87, 936-45.

Bíró, E. N. & Venyaminov, S. Y.

Depolymerization of actin in concentrated solutions of divalent metal chlorides.

Acta Biochim Biophys Acad Sci Hung 14, 31-42.

Actin transferred to concentrated (0.3-1.2 M) MgCl2 solutions depolymerizes completely. When protected by a high excess of ATP, actin in this MgCl2-depolymerized state is stable for several days in the cold. In the absence of excess ATP it slowly denatures. Chiroptical data and proteolysis experiments show that MgCl2-depolymerized actin is in a native, folded state, although its helix content is considerably decreased. By dissolving F-actin pellets or actin precipitated in paracrystalline state in concentrated MgCl2 solutions in the presence of ATP, very concentrated (100-200 mg/ml) monomeric actin solutions can be prepared. CaCl2 and MnCl2 have similar effects although these were not studied in detail.