Editing Histidine (section)

=== Degradation ===
Histidine is one of the amino acids that can be converted to intermediates of the tricarboxylic acid (TCA) cycle (also known as the citric acid cycle).<ref name="Swanson2010">{{cite book |last1=Swanson |first1=Todd A. |last2=Kim |first2=Sandra I. |last3=Glucksman |first3=Marc J. |last4=Lieberman |first4=Michael |last5=Swanson |first5=Todd A. |title=Biochemistry, molecular biology, and genetics |date=2010 |publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins |location=Philadelphia |isbn=9780781798754 |edition=5th}}{{Page needed|date=March 2025}}</ref> Histidine, along with other amino acids such as proline and arginine, takes part in deamination, a process in which its amino group is removed. In [[prokaryote]]s, histidine is first converted to urocanate by histidase. Then, urocanase converts urocanate to 4-imidazolone-5-propionate. Imidazolonepropionase catalyzes the reaction to form [[formiminoglutamate]] (FIGLU) from 4-imidazolone-5-propionate.<ref>{{Cite journal|last1=Coote|first1=J. G.|last2=Hassall|first2=H.|date=1973-03-01|title=The degradation of l-histidine, imidazolyl-l-lactate and imidazolylpropionate by Pseudomonas testosteroni|journal=Biochemical Journal|volume=132|issue=3|pages=409–422|issn=0264-6021|pmc=1177604|pmid=4146796|doi=10.1042/bj1320409}}</ref> The formimino group is transferred to [[tetrahydrofolate]], and the remaining five carbons form glutamate.<ref name="Swanson2010" /> Overall, these reactions result in the formation of glutamate and ammonia.<ref>{{Cite journal|last1=Mehler|first1=A. H.|last2=Tabor|first2=H.|date=1953-04-01|title=Deamination of histidine to form urocanic acid in liver|journal=The Journal of Biological Chemistry|volume=201|issue=2|pages=775–784|doi=10.1016/S0021-9258(18)66234-9|issn=0021-9258|pmid=13061415|doi-access=free}}</ref> Glutamate can then be deaminated by [[glutamate dehydrogenase]] or transaminated to form α-ketoglutarate.<ref name="Swanson2010" />