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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 ...
Animals obtain aromatic amino acids from their diet, but nearly [a] all plants and some micro-organisms must synthesize their aromatic amino acids through the metabolically costly shikimate pathway in order to make them. Histidine, phenylalanine, tryptophan, are essential amino acids for animals. Since they are not synthesized in the human body ...
"Histidine can be aromatic. When it is deprotonated, and uncharged, it is not aromatic. It no longer obeys Hückel's rule because 8 electrons are in the ring system (an extra two from the deprotonated nitrogen). Histidine obeys Hückel's rule when it is protonated, so then is aromatic." I am quite sure this is wrong.
Heteroarenes are aromatic compounds, where at least one methine or vinylene (-C= or -CH=CH-) group is replaced by a heteroatom: oxygen, nitrogen, or sulfur. [3] Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one ...
Lysine. Technically, any organic compound with an amine (–NH 2) and a carboxylic acid (–COOH) functional group is an amino acid. The proteinogenic amino acids are a small subset of this group that possess a central carbon atom (α- or 2-) bearing an amino group, a carboxyl group, a side chain and an α-hydrogen levo conformation, with the exception of glycine, which is achiral, and proline ...
Homochirality is a uniformity of chirality, or handedness.Objects are chiral when they cannot be superposed on their mirror images. For example, the left and right hands of a human are approximately mirror images of each other but are not their own mirror images, so they are chiral.
Hückel's rule can also be applied to molecules containing other atoms such as nitrogen or oxygen. For example, pyridine (C 5 H 5 N) has a ring structure similar to benzene, except that one -CH- group is replaced by a nitrogen atom with no hydrogen. There are still six π electrons and the pyridine molecule is also aromatic and known for its ...
Histidine decarboxylase is a group II pyridoxal-dependent decarboxylase, along with aromatic-L-amino-acid decarboxylase, and tyrosine decarboxylase. HDC is expressed as a 74 kDa polypeptide which is not enzymatically functional. [7] [8] Only after post-translational processing does the enzyme become active.