Essential amino acids are indispensable and are obtained from dietary proteins. The body utilizes amino acids for protein synthesis, energy production through oxidation and for non- protein function such as synthesis of bioactive molecules like dopamine (In Stipanuk,2013). Amino acids are essential for metabolic processes in the body. Deficiency of amino acids results in metabolic and developmental disorders. This article will focus on histidine and its metabolism. The article will explore the non-protein function of the amino acid in the body as well as pathways for synthesis of compounds from histidine.
Histidine is degraded to Tricyclic Acid Cycle intermediate glutamate which is then deaminated into alpha ketoglutarate (Gropper, Smith & Groff, 2009). Alpha ketoglutarate, a five carbon intermediate is then incorporated into the central pathway of intermediary metabolism. The amino group of histidine leaves as NH4 +. Another nitrogen group leaves later in the form of a formimino group yielding N5-formimino-THF. The transfer of formimino group results in glutamate intermediate.
Special Nonprotein Functions of Histidine
1. Regeneration of enzymes; histidine has a nitrogen atom on its side chain that captures and shuttles protons away from molecules resulting in opening up of receptor sites of the enzyme
2. Synthesis of histamine that is involved in allergic inflammatory conditions, immune responses in the body, acts as a neurotransmitter and is a regulator of physiological function requires intermediate synthesis into histamine.
3. It is essential for absorption and transport of iron, copper and zinc. Histidine is considered a metalloprotein that stimulates growth and thickening of bones, controls diarrhea and is involved in blood clotting.
4. The electron donating properties of histidine enables it to neutralize oxygen radicals consequently improved contractility of the heart, preservation of glutathione levels and protection against cellular and tissue damage brought about by the reactive oxygen species.
5. Histidine plays a role in the proper digestion of food by triggering the release of gastrin which is a digestive juice.
Compounds Synthesized From Histidine
II. Carnosine and related compounds anserine and homocarnosine
Synthetic Pathway of Histamine
According to Insel, Turner and Ross (2006), Histamine is synthesized through decarboxylation of histidine. Histidine decarboxylase catalyzes the reaction that results in the formation of histamine and carbon dioxide. Carnosine can be metabolized further into anserine and homocarnosine.
Synthetic Pathway Carnosine
Carnosine is synthesized from histidine and alanine through an energy-dependent reaction catalyzed by carnosine synthase as illustrated above.
Gropper, S. A. S., Smith, J. L., & Groff, J. L. (2009). Advanced nutrition and human metabolism. Australia: Wadsworth/Cengage Learning.
In Stipanuk, M. H., & In Caudill, M. A. (2013). Biochemical, physiological, and molecular aspects of human nutrition.
Insel, P. M., Turner, R. E., & Ross, D. (2006). Discovering nutrition. Sudbury, Mass: Jones and Bartlett Publishers.