Proposed mechanism for how MLCK diffusion on actin facilitates myosin phosphorylation during a contractile cycle. (A–E) See Fig. 6 for definition of cartoon elements and text for descriptions. Straight blue arrows indicate moving MLCK. Curved blue arrows and blue P on myosin heads indicate cycling phosphorylated myosin. The blue line at the bottom indicates the changes in Ca²⁺ concentration over time.