The binding of KRP to the neck region folded, ATP-bound dephosphorylated myosin also promotes unfolding and filament formation, thus looking like light chain phosphorylation. This could be a physiologically significant phenomenon considering the high concentration of ATP always present in smooth muscle cells. Thus, Kinase-related protein may have a very important role in relaxed smooth muscle by keeping dephosphorylated myosin in the filamentous state ready for the next rapid contractile response. Experiments aimed at testing this hypothesis indicated that under appropriate conditions a small excess of KRP is enough to form an equimolar complex with smooth muscle myosin and to cause its complete polymerization in the presence of ATP. Experiments where it has been tested this hypothesis, indicated that in appropriated conditions, a small excess of KRP is enough to form an equimolar complex with smooth muscle myosin and in the presence of ATP, cause its complete polymerization.