It is a semiessenzielle amino acid, which plays a central role in the organism. For children in the growth phase and people with renal insufficiency, the need for histidine is so high that it can be classified as an essential amino acid for this group of people.
What is histidine?
Histidine is one of the few basic amino acids besides arginine and lysine. At the same time it is also an aromatic amino acid with its imidazole ring. It occurs in two optically active forms. The enantiomer L-histidine represents the actual proteinogenic amino acid.
D-histidine has no biological significance. In the following, the term histidine always means only L-histidine. Overall, histidine contains six carbon atoms. Furthermore, it has two nitrogen atoms in the imidazole ring. In addition to the obligatory nitrogen in the alpha-terminal amino group, therefore, three nitrogen atoms are present in the total molecule. Due to the imidazole ring histidine reacts basic.
Histidine is present in two tautomeric forms because the hydrogen atom bound to nitrogen in the imidazole ring migrates back and forth between the two nitrogen atoms. The particular structure of the imidazole ring and the consequent basicity impart buffering properties to the histidine-containing proteins.
Function, effect & tasks
Histidine plays a central role in the organism. Since its isoelectric point is in the neutral range, histidine is the only amino acid that can function both as a proton acceptor and as a proton donor.
In addition to basic properties, it also has acidic properties at the same time. Because of this, histidine may participate in many enzymatic reactions involving proton transfer. Their central role is expressed in the so-called catalytic triad. The catalytic triad is a sequence of the amino acids aspartic acid, histidine and serine frequently found in enzymes. This structural unit catalyzes protein degradation by the hydrolytic cleavage of peptide bonds in proteins. Furthermore, histidine is used as the starting material for the red blood pigment hemoglobin.
Because it has good complexing properties, it forms complexes with iron within the histidine-containing proteins. This is what happens in ferritin and ensures its iron storage capacity within the organism. Due to its binding ability to heavy metals, it also detoxifies the body. Histidine also serves as a precursor for the synthesis of histamine. In this way, it provides for the strengthening of the immune system, as histamine is involved in the defense of foreign substances.
Histidine is also the starting material for the production of glutamate. It has great importance for the growth processes. Therefore, it represents an essential amino acid for adolescent children and adolescents. In addition, it supports wound healing and has an anti-inflammatory effect.
Education, occurrence, properties & optimal values
As already mentioned, histidine is actually a nonessential amino acid that can be produced by the body itself. However, the yield of the synthesis is so low that it must always be supplied to meet the needs of the food. That is why today we prefer to talk about semiessenzieller amino acid. In adolescent infants, however, external feeding is essential because the growth process requires large amounts of histidine. The same is true for severe conditions such as renal insufficiency.
However, healthy adults are given enough diet with histidine. Histidine deficiency is rare in Central Europe and can only be expected in extremely one-sided diets. Histidine in particular is present in chicken meat, salmon, nuts, soybeans, unpeeled rice, peas, milk or chicken eggs. Since these products or ingredients of these products are present in almost all foods, an adequate supply of histidine should generally be ensured. However, even with a lower intake of histidine, the body's own production does not increase.
Diseases & Disorders
Due to the central role of histidine, its deficiency or impaired breakdown of histidine breakdown products such as histamine can lead to various health conditions. In certain diseases, too low histidine concentrations are found in the organism.
This applies to chronic renal insufficiency or rheumatoid arthritis. It was found that increased intake of histidine has a positive influence on rheumatoid arthritis. As part of its central role in metabolism, it has anti-inflammatory effects, so that the strong inflammatory processes are severely restricted. Even with severe injuries and trauma, the need for histidine is increased. Too low a concentration leads to a delayed wound healing. If too little histidine is added in the growth phase, it leads to growth disorders. Histidine is a good radical scavenger and therefore has the potential to slow down degenerative processes.
Furthermore, the positive effect of histidine on hypertension and infections was recognized. The blood pressure can be lowered in the long term and the duration of a cold can be significantly reduced. There is a genetic condition in which the breakdown of histidine is disrupted. However, the autosomal recessive hereditary disease called histidineemia usually causes no symptoms, so treatment is usually unnecessary. However, under unusual conditions central nervous symptoms may appear. Then a histidine-poor diet is recommended. In patients with stress, anxiety disorders or schizophrenia, very high levels of histidine were found.
Overall, however, the increased concentration of a synthesis product of histidine, the histamine, plays a greater role in disease processes. Histamine is an active ingredient that causes a variety of symptoms in breakdown disorders such as autoimmune disorders, allergies, cardiovascular diseases or gastrointestinal disorders. For treatment histamine-rich foods should be avoided. However, foods high in histamine content also have high levels of histidine.