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Histidine ball and stick model spinning. Histidine (symbol His or H) [2] is an essential amino acid that is used in the biosynthesis of proteins.It contains an α-amino group (which is in the protonated –NH 3 + form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO − form under biological conditions), and an imidazole side chain (which is partially ...
The triad is exemplified by chymotrypsin, [c] a model serine protease from the PA superfamily which uses its triad to hydrolyse protein backbones. The aspartate is hydrogen bonded to the histidine, increasing the pK a of its imidazole nitrogen from 7 to around 12. Histidine is thus able to act as a powerful general base, activating the serine ...
Imidazole is the side chain of histidine and is typically used at a concentration of 150 - 500 mM for elution. Histidine or histamine can also be used. Decrease in pH; When the pH decreases, the histidine residue is protonated and can no longer coordinate the metal tag, allowing the protein to be eluted.
However, a quadrupole-ion model system cannot be used to quantitatively model cation–π interactions. Such models assume point charges, and are therefore not valid given the short cation–π bond distance. In order to use electrostatics to predict energies, the full electrostatic potential surface must be considered, rather than just the ...
A conservative replacement (also called a conservative mutation or a conservative substitution or a homologous replacement) is an amino acid replacement in a protein that changes a given amino acid to a different amino acid with similar biochemical properties (e.g. charge, hydrophobicity and size). [1] [2]
Diagram of electrospray ionization in positive mode: under high voltage, the Taylor cone emits a jet of liquid drops. The solvent from the droplets progressively evaporates, leaving them more and more charged. When the charge exceeds the Rayleigh limit the droplet explosively dissociates, leaving a stream of charged (positive) ions
In chemistry, a zwitterion (/ ˈ t s v ɪ t ə ˌ r aɪ ə n / TSVIT-ə-ry-ən; from German Zwitter 'hermaphrodite'), also called an inner salt or dipolar ion, [1] is a molecule that contains an equal number of positively and negatively charged functional groups. [2] 1,2-dipolar compounds, such as ylides, are sometimes excluded from the ...
Histidine tags have an affinity for nickel, cobalt, zinc, copper and iron ions which have been immobilized by forming coordinate covalent bonds with a chelator incorporated in the stationary phase. For elution, an excess amount of a compound able to act as a metal ion ligand, such as imidazole, is used. GST has an affinity for glutathione which ...