 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
NCP Miracle II
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
| L-Histidine |
L-Histidine
One of the 20 most common natural amino acids present in proteins.
In the nutritional sense, in humans, histidine is considered an
essential amino acid, but mostly only in children. Its codons are CAU
and CAC. The imidazole side chains and the relatively neutral pKa of
histidine (ca 6.0) mean that relatively small shifts in cellular pH will
change its charge. For this reason, this amino acid side chain finds
its way into considerable use as a coordinating ligand in
metalloproteins, and also as a catalytic site in certain enzymes. The
imidazole side chain has two nitrogens with different properties: One
is bound to hydrogen and donates its lone pair to the aromatic ring
and as such is slightly acidic, whereas the other one donates only
one electron pair to the ring so it has a free lone pair and is basic.
These properties are exploited in different ways in proteins. In
catalytic triads, the basic nitrogen of histidine is used to abstract a
proton from serine, threonine or cysteine to activate it as a
nucleophile. In a histidine proton shuttle, histidine is used to quickly
shuttle protons, it can do this by abstracting a proton with its basic
nitrogen to make a positively-charged intermediate and then use
another molecule, a buffer, to extract the proton from its acidic
nitrogen. In carbonic anhydrases, a histidine proton shuttle is utilized
to rapidly shuttle protons away from a zinc-bound water molecule to
quickly regenerate the active form of the enzyme.
Because of histidine's affinity for metal ions, researchers will often
add a polyhistidine-tag to a protein of interest. The metal affinity can
then be used to purify, detect, or immobilize the protein to be studied
One of the 20 most common natural amino acids present in proteins.
In the nutritional sense, in humans, histidine is considered an
essential amino acid, but mostly only in children. Its codons are CAU
and CAC. The imidazole side chains and the relatively neutral pKa of
histidine (ca 6.0) mean that relatively small shifts in cellular pH will
change its charge. For this reason, this amino acid side chain finds
its way into considerable use as a coordinating ligand in
metalloproteins, and also as a catalytic site in certain enzymes. The
imidazole side chain has two nitrogens with different properties: One
is bound to hydrogen and donates its lone pair to the aromatic ring
and as such is slightly acidic, whereas the other one donates only
one electron pair to the ring so it has a free lone pair and is basic.
These properties are exploited in different ways in proteins. In
catalytic triads, the basic nitrogen of histidine is used to abstract a
proton from serine, threonine or cysteine to activate it as a
nucleophile. In a histidine proton shuttle, histidine is used to quickly
shuttle protons, it can do this by abstracting a proton with its basic
nitrogen to make a positively-charged intermediate and then use
another molecule, a buffer, to extract the proton from its acidic
nitrogen. In carbonic anhydrases, a histidine proton shuttle is utilized
to rapidly shuttle protons away from a zinc-bound water molecule to
quickly regenerate the active form of the enzyme.
Because of histidine's affinity for metal ions, researchers will often
add a polyhistidine-tag to a protein of interest. The metal affinity can
then be used to purify, detect, or immobilize the protein to be studied