**Question:** Active GP consists of

A. Enzymatic activation
B. Receptor binding
C. Direct pharmacological effect
D. Membrane potential alteration

**Correct Answer:** D. Membrane potential alteration

**Core Concept:**
Active G protein-coupled receptors (GPCRs) are a subclass of GPCRs that mediate intracellular signaling by directly altering the membrane potential (M.P.) of the target cell. These receptors are involved in various physiological processes and play a crucial role in the transmission of signals within the cell.

**Why the Correct Answer is Right:**
Active GP (G protein-coupled receptors) function by coupling to G proteins, which in turn triggers a cascade of intracellular events leading to a change in M.P. of the target cell. This alteration in M.P. is the direct result of the activation of the GPCR and signifies the activation of the receptor.

**Why Each Wrong Option is Incorrect:**
A. Enzymatic activation (Option A) is not a primary mechanism of action for active GP. Instead, they usually involve G protein coupling and subsequent intracellular signaling pathways.

B. Receptor binding (Option B) refers to the interaction between an active GP and its ligand, but it does not explain the subsequent cellular response.

C. Direct pharmacological effect (Option C) is a broader term than active GP and does not specifically describe the mechanism of action of altering M.P. via G protein coupling.

**Clinical Pearl:** Understanding the mechanism of action of active GP is essential for comprehending their role in cellular signaling and therapeutic interventions targeting these receptors. Active GP is involved in various physiological processes, including neurotransmission, hormone signaling, and immune response regulation.