Ans. (C) Insulin binds to a transmembrane receptor at the outer surface of the plasma membrane, which activates the tyrosine kinase that is the cytosolic domain of the receptor.(KDT 8th/e p58)Enzymatic Receptors have two sites, the drug binds on the extracellular site and the intracellular site has enzymatic activity (mostly tyrosine kinase). This enzyme can be activated via JAK-STAT pathway. Insulin, growth hormone, prolactin and cytokines act via enzymatic receptors.