histidine (hĭs`tĭdēn), organic compound, one of the 22 α-amino acids amino acid (əmē`nō)
..... Click the link for more information. commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. Histidine is the direct precursor of histamine histamine (hĭs`təmēn')
..... Click the link for more information. ; it is also an important source of carbon atoms in the synthesis of purines purine, type of organic base found in the nucleotides and nucleic acids of plant and animal tissue. The German chemist Emil Fischer did much of the basic work on purines and introduced the term into the chemical literature in the early 20th cent.
..... Click the link for more information. . The imidazole group on the side chain of histidine can act as both an acid and a base, i.e., it can both donate and accept protons under some conditions. This turns out to be an important property when histidine is incorporated into proteins protein, any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
..... Click the link for more information. , particularly when it becomes a part of the primary structure of some enzymes enzyme, biological catalyst . The term enzyme comes from zymosis, the Greek word for fermentation , a process accomplished by yeast cells and long known to the brewing industry, which occupied the attention of many 19th-century chemists.
..... Click the link for more information. . It is thought that the side chain of this amino acid acts as a general acid and base as it participates in the catalytic functions of chymotrypsin chymotrypsin (kī'mōtrĭp`sĭn), proteolytic, or protein-digesting, enzyme active in the mammalian intestinal tract.
..... Click the link for more information. , as well as those of a number of enzymes dealing with the metabolism of carbohydrates, proteins, and nucleic acids. It has even been implicated in the workings of cocoonase, the enzyme that allows adult silk moths to escape from their cocoons. Histidine is considered to be an essential amino acid for infants (it must be supplied in the diet); experiments with adults indicate that they can go for at least short periods without dietary intake of this amino acid. It was isolated from protein in 1896; its structure was confirmed by chemical synthesis in 1911.

histidine

One of the essential amino acids, first isolated in 1896. It occurs abundantly in hemoglobin and can be isolated from blood cells. It is used in medicine and biochemical research and as a dietary supplement and feed additive.

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histidine

histidine