The main difference between histidine and histamine is that histidine is an essential amino acid found in most animal proteins whereas histamine is an amine formed by the decarboxylation of histidine.
Histidine and histamine are two related compounds which perform distinct functions in the body. That is; histidine is important in tissue growth and repair while the body releases histidine during allergic reactions.
Key Areas Covered
1. What is Histidine
– Definition, Structure, Role
2. What is Histamine
– Definition, Structure, Role
3. What are the Similarities Between Histidine and Histamine
– Outline of Common Features
4. What is the Difference Between Histidine and Histamine
– Comparison of Key Differences
Key Terms
Allergic Reactions, Amine, Amino Acid, Decarboxylation, Histamine, Histidine, Protein Synthesis
What is Histidine
Histidine is an alpha-amino acid required in protein synthesis. It contains a protonated amine group (NH3+) and a deprotonated carboxylic group (COO–) under biological conditions. It also contains a partially protonated imidazole side chain. Based on the charge on the side chain, histidine is considered as a positively-charged amino acid under physiological conditions.
Figure 1: Histidine
Both microorganisms and plants can synthesize histidine in the pentose phosphate pathway. However, humans cannot synthesize this amino acid in the body by de novo biochemical reactions. Therefore, it becomes an essential amino acid, which the body has to intake from the diet. Furthermore, histidine occurs in banana, grapes, poultry, meat, and milk.
Figure 2: Heme Group inside Succinate Dehydrogenase
Moreover, histidine is a major amino acid readily converted to the intermediate compounds of the TCA cycle inside the body. Also, it undergoes deamination, which removes the amine group. One of the key function of the imidazole ring of histidine in polypeptide chains is in stabilizing the folded structures. Also, histidine is important in the regulation of trace elements including iron, copper, zinc, molybdenum, and manganese.
What is Histamine
Histamine is an amine synthesized in the body. Histidine serves as the precursor for the synthesis of histamine in a biochemical reaction known as decarboxylation. Here, the L-histidine decarboxylase is the enzyme responsible for this conversion by removing the carboxylic acid group from the histidine. Furthermore, the body stores some amount of histamine while the rest undergoes enzymatic inactivation. Production of most of the storing histamines takes place inside the granules of mast cells and basophils. The release of histamine by these cells is immunogenic as histamine serves as an inflammatory agent during allergic reactions. The IgE antibodies-bound mast cells and basophils release histamine when exposed to the appropriate antigen. Then the released histamines are responsible for the dilation of capillaries, contraction of smooth muscles, and stimulation of gastric acid secretions. Histamines also serves as a neurotransmitter in the brain, spinal cord, and in the uterus.
Figure 3: Histidine Decarboxylation
For instance, aged, as well as fermented food, high-protein food, and alcohols like red wine, may contain higher amounts of histamine, which can cause histamine poisoning and food allergy.
Similarities Between Histidine and Histamine
- Histidine and histamine are two related compounds.
- Moreover, they are organic, nitrogenous compounds.
- Also, both contain an imidazole ring and amine group.
- Besides, both perform distinct functions in the body.
Difference Between Histidine and Histamine
Definition
Histidine refers to a basic amino acid and is a constituent of most proteins. Also, it is an essential nutrient in the diet of vertebrates and is the source from which the body derives histamine. Whereas, histamine refers to a compound released by the cells in response to injury and allergic and inflammatory reactions. And, this compound causes the contraction of smooth muscle and dilation of capillaries. Hence, we can interpret the main difference between histidine and histamine from these definitions.
Type of Compound
A difference between histidine and histamine is that the histidine is an amino acid while the histamine is an amine.
Chemical Formula
Moreover, histidine is C6H9N3O2 while histidine is C5H9N3.
Carboxylic Group
Furthermore, another difference between histidine and histamine is that the histidine contains a carboxylic group while the histamine does not contain a carboxylic group.
Significance
Histidine is an essential amino acid, which the body cannot produce while the body produces histamine from histidine inside the body through decarboxylation. Hence, this is an important difference between histidine and histamine.
Function
Another difference between histidine and histamine is their function. Histidine is important for the growth and repair of tissues while the body releases histamine during allergic reactions.
Conclusion
Histidine is an essential, alpha-amino acid, which is important for protein synthesis. Histidine residues regulate trace elements inside the polypeptide chain while stabilizing the folded proteins. On the other hand, histamine is an amine produced from histidine. It serves as an inflammatory agent, which mediate allergic reactions. The main difference between histidine and histamine is their structure and role in the body.
Reference:
1. “Histidine.” Amino Acids – Structure, Advantages, Properties, Classification, Available Here
2. “What Are Histamines?” WebMD, Available Here
Image Courtesy:
1. “L-Histidine physiological” By Vaccinationist – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Succinate Dehygrogenase 1YQ3 Haem group” By The original uploader was Zephyris at English Wikipedia. (CC BY-SA 3.0) via Commons Wikimedia
3. “Histidine decarboxylase” By S. Jähnichen – Own work (Public Domain) via Commons Wikimedia
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