- Thiophosphorylation of the 130-kDa subunit is associated with a decreased activity of myosin light chain phosphatase in alpha-toxin-permeabilized smooth muscle. Trinkle-Mulcahy, L., Ichikawa, K., Hartshorne, D.J., Siegman, M.J., Butler, T.M. J. Biol. Chem. (1995)