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Arginine: Its p K a value revisited
Author(s) -
Fitch Carolyn A.,
Platzer Gerald,
Okon Mark,
GarciaMoreno E. Bertrand,
McIntosh Lawrence P.
Publication year - 2015
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.2647
Subject(s) - protonation , chemistry , arginine , moiety , dissociation constant , side chain , dissociation (chemistry) , electrostatics , acid dissociation constant , membrane , crystallography , nuclear magnetic resonance spectroscopy , stereochemistry , computational chemistry , amino acid , ion , organic chemistry , biochemistry , receptor , aqueous solution , polymer
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.