Protein Kinases Are Enzymes That Transfer the Terminal Phosphate from ATP

Multiple Choice

Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localisation?

A) ATP is more abundant near the plasma membrane.
B) They can more readily encounter and phosphorylate other membrane proteins.
C) Membrane localisation lowers the activation energy of the phosphorylation reaction.
D) They flip back and forth across the membrane to access target proteins on either side.