The kinetic properties of smooth muscle: How a little extra weight makes myosin faster

The contractile properties of smooth muscle (SM) are often described as fast and slow, but the molecular basis for the diversity in contractile properties has yet to be fully elucidated. Studies have shown that the differences in the contractile parameters are seen at the level of the contractile proteins. Experiments have implicated both the splicing of the SM myosin heavy chain (MHC) and the SM myosin essential myosin light chain as possible molecular determinants of the contractile properties of SM. This communication will focus on the role of the 7 aa insert in the smooth muscle MHC in determining the contractile properties of SM and the possible mechanism by which this insert could alter the kinetics of the SM actomyosin ATPase.