Figure 23.

(A) Electrostatic surface potential and hydrogen-bonding donor sites of the side chain of arginine, and the methylated arginine side chains of MMA, ADMA, and SDMA. C_α denotes the α-carbon. Charge potentials were rendered by using SPARTAN (Wavefunction Inc.), with negative electrostatic charges shown in red, positive charges in blue, and neutral charges in green. (B) Distinct stereoisomers for MMA and SDMA. Methyl groups are highlighted in yellow, whereas hydrogen-bonding donor sites are marked in red. Stereoisomers emerging from rotation around the central C_ζ–N_ε bond are omitted for simplicity.