How does the binding of GTP and GDP regulate the activity of G proteins?

• A. G proteins are activated by ATP binding and inactivated by ADP binding.
• B. G proteins are activated by GTP binding and inactivated by GDP binding.
• C. G proteins are activated by ADP binding and inactivated by ATP binding.
• D. G proteins are activated by GDP binding and inactivated by GTP binding.

Answer: (B)