Subunit exchange between smooth muscle myosin filaments.
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.
Trybus
K M
KM
Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254.
Lowey
S
S
D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism; D008854:Microscopy, Electron; D009130:Muscle, Smooth / Q000378:metabolism* / Q000648:ultrastructure; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation
D009218:Myosins