What is the Difference Between Histidine and Histamine?

Histidine and histamine are two different organic compounds that play essential roles in human physiology. The key differences between them are:

1. Type of Compound: Histidine is an α-amino acid used in the biosynthesis of proteins, while histamine is an amine that acts as a neurotransmitter for the brain, spinal cord, and uterus.
2. Structure: Histidine has a molecular formula of C6H9N3O2, whereas histamine has a molecular formula of C5H9N3.
3. Role in the Body: Histidine is essential for growth, tissue repair, and the maintenance of myelin sheaths that protect nerve cells. It is also required for blood cell manufacture and protects tissue against free radicals. On the other hand, histamine is an inflammatory agent that mediates allergic reactions and is produced from histidine through a process involving the enzyme histidine ammonia-lyase.
4. Reactions with Ortho-Phthalaldehyde (OPA): Histidine and histamine exhibit different reaction pathways when reacting with OPA. Histamine reacts with OPA in an alkaline medium to form an unstable fluorescent adduct (Fbase-Hm), which becomes stable and highly fluorescent after acidification. In contrast, histidine develops a relatively stable fluorescent adduct (Fbase-Hd) with OPA in an alkaline medium, and upon acidification, it forms an unstable adduct.

Comparative Table: Histidine vs Histamine

Here is a table highlighting the differences between histidine and histamine:

Please note that the Differences and Similarities sections are the same as those provided in the search results.