Proteins can be covalently modified by the addition of phosphate groups to all but which of the following amino acids?
A) Arginine
B) Threonine
C) Serine
D) All of the above

Question

Quizplus · Accepted Answer

Arginine cannot be phosphorylated because it does not have a hydroxyl group (-OH) on its side chain that can participate in a phosphorylation reaction. Threonine and serine, on the other hand, have hydroxyl groups on their side chains that can undergo phosphorylation.

Proteins Can Be Covalently Modified by the Addition of Phosphate