Pressure-jump studies on the length-regulation kinetics of the self-assembly of myosin from vertebrate skeletal muscle into thick filament.

The self-assembly of myosin monomer into thick filament occurs via a two-step mechanism. At first a pair of myosin monomers reacts to form a parallel dimer; the dimer in turn adds to the filament ends at a rate that is independent of filament length. The rate of the dissociation reaction on the other hand is length-dependent. The 'off' rate constant has been shown to increase exponentially by a factor of 500 as the filament grows from the bare-zone out to its full length. The length of the filament is thus kinetically controlled; myosin is added to the filament at a fixed rate, whereas the dissociation rate increases to a point where equilibrium is established and the filament ceases to grow. The structural implications implicit in the mechanism are discussed.