Arginine: Its pKa value revisited. (22nd March 2015)

• Record Type: Journal Article
• Authors: Fitch, Carolyn A.; Platzer, Gerald; Okon, Mark; Garcia‐Moreno E., Bertrand; McIntosh, Lawrence P.
• Is Part Of: Protein science. Volume 24:Number 5(2015:May)
• Page Start: 752
• Page End: 761
• Publication Date: 2015-03-22
• Subjects: protein electrostatics -- pH titration -- equilibrium acid dissociation constant -- pKa value -- guanidinium -- tautomer -- potentiometry -- NMR spectroscopy; Proteins -- Periodicals; 572.6
• DOI: 10.1002/pro.2647
• Languages: English
• ISSNs: 0961-8368

Abstract

Abstract: Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (p K a 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 p K a value helps explains why arginine side chains in proteins are always predominantly charged, even at pH values as great as 10. The high p K a 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.