Subunit exchange between smooth muscle myosin filaments
Trybus, K.M.; Lowey, S.
Progress in Clinical and Biological Research 245: 81-90
1987
ISSN/ISBN: 0361-7742 PMID: 3685024 Document Number: 289888
Myosin filaments are in equilibrium with a "critical concentration" of monomer (Josephs & Harrington, 1966). Our recent studies with smooth muscle myosin minifilaments and larger synthetic filaments suggest that this monomer pool undergoes more extensive exchange with the polymer than would occur if only polymer ends were involved. This observation provides a possible explanation for the behavior of copolymers of dephosphorylated and phosphorylated myosin in the presence of nucleotide. Upon addition of 1 mM MgATP, essentially all of the dephosphorylated myosin disassembled to the folded monomeric conformation, despite the presence of the more stable phosphorylated molecules in the same polymer. If molecules exchange freely in and out of the filament, phosphorylated myosin would not be expected to exert a significant stabilizing influence on neighboring dephosphorylated molecules.