Salt bridges: Difference between revisions

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 <applet load='1cbr' size='300' frame='true' align='right' caption='Salt bridge between retinoic acid(-) and arg131(+) in [[1cbr]].'
 scene='Salt_bridges/Salt_bridge/1' />
-In proteins, salt bridges occur between amino acid side-chains with opposite positive or negative full-electron charges, namely, (at neutral pH) Glu- or Asp- vs. Arg+ or Lys+. They may also occur between ionized organic ligands, such as acetylcholine+ (or example at right: [[1cbr]]), or inorganic ions, such as K+ or Cl-, and amino acid side-chains.
+In proteins, salt bridges occur between amino acid side-chains with opposite positive or negative full-electron charges, namely, (at neutral pH) Glu- or Asp- vs. Arg+ or Lys+. They may also occur between ionized organic ligands, such as acetylcholine+ (or example at right: [[1cbr]]), or inorganic ions, such as K<sup>+</sup> or SO<sub>4</sub><sup>=</sup>, and amino acid side-chains.
 A salt bridge is generally considered to exist when the centers of charge are 4 &Aring; or less apart<ref>Jeffrey, George A., An introduction to hydrogen bonding, Oxford University Press, 1997. Page 192.</ref>. The center of charge of the arginine sidechain is the zeta carbon<ref name='GD'>PMID: 10449714</ref>. The energetic significance of such complementary charge pairs is a complex function of the local environment.