Which enzyme hydrolyzes cGMP during phototransduction?

Which enzyme hydrolyzes cGMP during phototransduction?

• A. Adenylyl cyclase
• B. Guanylate cyclase
• C. Phosphodiesterase
• D. Protein kinase A

Answer: (C)

In phototransduction, a key step is lowering the level of the signaling molecule cGMP. This happens when an enzyme called phosphodiesterase hydrolyzes cGMP to GMP. In rods and cones, light-activated rhodopsin activates the G-protein transducin, which in turn activates PDE6. The resulting drop in cGMP causes the cGMP-gated ion channels to close, leading to hyperpolarization of the photoreceptor and reduced neurotransmitter release. Adenylyl cyclase would produce cAMP from ATP, not hydrolyze cGMP. Guanylate cyclase makes cGMP from GTP. Protein kinase A is a downstream effector of cAMP signaling and does not hydrolyze cGMP.

In phototransduction, a key step is lowering the level of the signaling molecule cGMP. This happens when an enzyme called phosphodiesterase hydrolyzes cGMP to GMP. In rods and cones, light-activated rhodopsin activates the G-protein transducin, which in turn activates PDE6. The resulting drop in cGMP causes the cGMP-gated ion channels to close, leading to hyperpolarization of the photoreceptor and reduced neurotransmitter release.

Adenylyl cyclase would produce cAMP from ATP, not hydrolyze cGMP. Guanylate cyclase makes cGMP from GTP. Protein kinase A is a downstream effector of cAMP signaling and does not hydrolyze cGMP.