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Aspartic acid has an acidic side chain (CH 2 COOH) which reacts with other amino acids, enzymes and proteins in the body. [5] Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO − . [ 5 ]
The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains. The pK a values of an amino acid side chain in solution is typically inferred from the pK a values of model compounds (compounds that are similar to the ...
Amino acid Short Abbrev. Side chain Hydro-phobic pKa § Polar pH Small Tiny Aromatic or Aliphatic van der Waals volume (Å 3) Alanine: A Ala -CH 3 - - Aliphatic 67 Cysteine: C Cys -CH 2 SH: 8.55 acidic - 86 Aspartic acid: D Asp -CH 2 COOH 3.67 acidic - 91 Glutamic acid: E Glu -CH 2 CH 2 COOH 4.25 acidic - 109 Phenylalanine: F Phe -CH 2 C 6 H 5 ...
The aspartic acid side chain has a pKa of approximately 4. In an acidic environment, this residue will readily give up its proton, but will also take a proton away from water if the side chain is deprotonized, thus catalyzing the hydroxyl attack on the phosphate group.
The N-O distance required is less than 4 Å (400 pm). Amino acids greater than this distance apart do not qualify as forming a salt bridge. [11] Due to the numerous ionizable side chains of amino acids found throughout a protein, the pH at which a protein is placed is crucial to its stability.
The side-chain of the nucleophilic residue performs covalent catalysis on the substrate. The lone pair of electrons present on the oxygen or sulfur attacks the electropositive carbonyl carbon. [3] The 20 naturally occurring biological amino acids do not contain any sufficiently nucleophilic functional groups for many difficult catalytic ...
Asparagine also provides key sites for N-linked glycosylation, modification of the protein chain with the addition of carbohydrate chains. Typically, a carbohydrate tree can solely be added to an asparagine residue if the latter is flanked on the C side by X-serine or X-threonine, where X is any amino acid with the exception of proline. [19]
It consists of three amino acid residues (labeled i, i+1 and i+2) in which residue i is an aspartate (Asp) or asparagine (Asn) that forms a hydrogen bond from its sidechain CO group to the mainchain NH group of residue i+2. About 14% of Asx residues present in proteins belong to Asx turns.
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