Binding of pseudosubstrate to protein kinase A. Notice that the inhibitor makes multiple contacts with the enzyme. The two arginine side chains of the pseudosubstrate ionically interact with three glutamate carboxylate groups (green dashed lines). Hydrophobic interactions also are important in the recognition of substrate. The isoleucine residue of the pseudosubstrate is in contact with a pair of leucine residues of the enzyme.