Rho-associated kinase (Rho-kinase) phosphorylates myosin light chain (MLC) at serine 19, the same site phosphorylated by MLC kinase. Rho-kinase is activated by GTP-Rho and subsequently phosphorylates MLC, which enhances the actin activation of myosin ATPase, leading to smooth muscle contraction. Rho-kinase is a serine/threonine kinase that is activated by Rho and interacts with myosin phosphatase to inactivate it, thereby increasing MLC phosphorylation. This process is crucial for Rho's role in regulating cytokinesis, cell motility, and smooth muscle contraction. Rho-kinase is ubiquitously expressed in various tissues and is involved in the regulation of phosphatidylinositol 3-kinase, phosphatidylinositol 4-phosphate-5-kinase, and c-fos expression. The study shows that Rho-kinase phosphorylates MLC in a GTP-Rho-dependent manner, and this phosphorylation is essential for the activation of myosin ATPase and subsequent muscle contraction. The results indicate that Rho-kinase functions similarly to MLC kinase in phosphorylating MLC, but with a lower molecular activity. The study also demonstrates that Rho-kinase phosphorylates MLC at Ser-19, which is essential for actin activation of myosin ATPase. These findings suggest that Rho-kinase plays a key role in the regulation of MLC phosphorylation and muscle contraction.Rho-associated kinase (Rho-kinase) phosphorylates myosin light chain (MLC) at serine 19, the same site phosphorylated by MLC kinase. Rho-kinase is activated by GTP-Rho and subsequently phosphorylates MLC, which enhances the actin activation of myosin ATPase, leading to smooth muscle contraction. Rho-kinase is a serine/threonine kinase that is activated by Rho and interacts with myosin phosphatase to inactivate it, thereby increasing MLC phosphorylation. This process is crucial for Rho's role in regulating cytokinesis, cell motility, and smooth muscle contraction. Rho-kinase is ubiquitously expressed in various tissues and is involved in the regulation of phosphatidylinositol 3-kinase, phosphatidylinositol 4-phosphate-5-kinase, and c-fos expression. The study shows that Rho-kinase phosphorylates MLC in a GTP-Rho-dependent manner, and this phosphorylation is essential for the activation of myosin ATPase and subsequent muscle contraction. The results indicate that Rho-kinase functions similarly to MLC kinase in phosphorylating MLC, but with a lower molecular activity. The study also demonstrates that Rho-kinase phosphorylates MLC at Ser-19, which is essential for actin activation of myosin ATPase. These findings suggest that Rho-kinase plays a key role in the regulation of MLC phosphorylation and muscle contraction.