Metal binding to myosin and to myosin DTNB-light chain

The effects of various divalent cations, Ca2+, Mg2+ and Mn2+ on the intrinsic fluorescence of heavy meromyosin (HMM) and myosin 5,5'-dithio-bis-(2-nitrobenzoate) DTNB-light chain of rabbit striated muscle, are compared. At pH 6.4, th fluorescence change induced by the metal ions is present only in the isolated light chain and disappears in HMM, thus indicating an interaction between the heavy and light chains with respect to the binding of the metal ions. Whereas Mg2+ binds more strongly than Ca2+ to myosin, this order is reversed in the case of the DTNB-light chain.