Inhibitory effect of MgATP on the release of regulatory light chain from scallop myosin and light chain composition of scallop myosin hybridized with abalone light chain 2 at 30 degrees C

The experimental conditions for release of the regulatory light chain (RLC) of scallop myosin at 30 degrees C were studied. Substantially all RLC was released from myosin by incubation for 5 min in medium containing buffer and KCl. This release of RLC was inhibited strongly by Ca2+, while the effect of Mg2+ was about 10,000 times weaker than that of Ca2+. Even in the absence of Ca2+, MgATP and MgADP inhibited the release of RLC, while the protective effect of AMPPNP was negligible. Other Mg nucleotides also showed some protective effect, though appreciably less than MgATP. The incubation of scallop myosin with abalone regulatory light chain (LC2) at 30 degrees C for 5 min produced a hybrid myosin. In the presence of 5 mM MgCl2, 1 of the 2 mol of RLC per mol of scallop myosin was exchanged with 1 mol of LC2. In the presence of Ca2+ or MgATP, myosin bound 1 extra mole of LC2 besides the 2 mol each of SH-LC and RLC.