Final answer:
The enzyme activated by both GPCRs and RTKs is Phospholipase C (option A), which is involved in the cell signaling cascade leading to various cellular responses.
Step-by-step explanation:
The enzyme activated by both G Protein-Coupled Receptors (GPCRs) and Receptor Tyrosine Kinases (RTKs) is Phospholipase C. GPCRs activate Phospholipase C through a G-protein-mediated pathway, wherein an effector signal molecule binds to a receptor, activating the integral membrane Phospholipase C enzyme.
This enzyme catalyzes the formation of cytosolic inositol triphosphate (IP3) and membrane-bound diacylglycerol (DAG), which play a role in the cell signaling cascade. RTKs also lead to the activation of Phospholipase C through different mechanisms involving phosphorylation and recruitment of adaptor proteins. In contrast, adenylyl cyclase is activated by GPCRs but is not a point of convergence for RTK signaling. Therefore, the correct answer is A. Phospholipase C.