title: Arginine: Its pKa value revisited.
abstract: Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (pKa value) of the arginine guanidinium group is 13.8 ± 0.1. This is substantially higher than that of ∼ 12 often used in structure-based electrostatics calculations and cited in biochemistry textbooks. The revised intrinsic pKa value helps explains why arginine side chains in proteins are always predominantly charged, even at pH values as great as 10. The high pKa value also reinforces the observation that arginine side chains are invariably protonated under physiological conditions of near neutral pH. This occurs even when the guanidinium moiety is buried in a hydrophobic micro-environment, such as that inside a protein or a lipid membrane, thought to be incompatible with the presence of a charged group.
authors: Department of Biophysics, Johns Hopkins University, Baltimore, Maryland, 21218.
authors: Carolyn A
authors: CA
authors: Fitch
authors: Gerald
authors: G
authors: Platzer
authors: Mark
authors: M
authors: Okon
authors: Bertrand E
authors: BE
authors: Garcia-Moreno
authors: Lawrence P
authors: LP
authors: McIntosh
mesh_terms: D000143:Acids / Q000737:chemistry*; D001120:Arginine / Q000737:chemistry*; D001665:Binding Sites; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011506:Proteins / Q000737:chemistry*
chemical_list: D000143:Acids; D008051:Lipid Bilayers; D011506:Proteins; D001120:Arginine
keywords: NMR spectroscopy; equilibrium acid dissociation constant; guanidinium; pH titration; pKa value; potentiometry; protein electrostatics; tautomer