THE HDC PROTEIN
The HDC [histidine decarboxylase] protein is an enzyme in humans. An enzyme is a specific protein that is biologically activated within the body. Many enzymes catalyze or aid in biochemical reactions that take place in cells [1]. In this case, the HDC protein catalyzes the conversion of histidine to histamine which involves the cleavage, or removal, of carbon dioxide as seen in Figure 1. HDC is encoded by a single copy gene known as the Hdc gene. It contains 662-amino acids, which are the building blocks of all proteins [6]. To the left you will see the the folded protein model of HDC. |
HISTAMINE
Histamine is an important part of many processes within the human body including neurotransmission, gastric acid secretion and smooth muscle tone [2]. Once converted from histidine, it is either stored or inactivated. There are two common human histamines, mast cell histamines and non-mast cell histamines. Mast cell histamines are the mediators in the inflammatory response system, refer to Figure 2, while non-mast cell histamines are found within brain tissue [3].
Mast cell histamines are commonly known as a trigger for the inflammatory response. Antibodies catered to a certain allergen attach themselves to mast cells. When an allergen specific to those antibodies enters the body, the mast cell releases histamines. Histamines dilate the blood vessels and fill the surrounding cells with fluid. This brings the onset of many symptoms including hives, itchy body, eyes and nose, wheezing, nausea, diarrhea and vomiting [5].
The non-mast cell histamine within the brain is much more complex, refer to Figure 3. As well as having a role in arousal, cognitive functions, and hormone secretion the histamine systems play a part in neurological and psychiatric disease [4]. Alzheimer's and Tourette Syndrome patients have been found to have lower levels of histamine where Parkinson's and schizophrenic patients have been found to have high levels of histamine. The low histamine levels are known to be associated with the onset of convulsions and seizures. As seen in Tourette Syndrome, motor tics are less severe forms of convulsions and seizures [4].
Mast cell histamines are commonly known as a trigger for the inflammatory response. Antibodies catered to a certain allergen attach themselves to mast cells. When an allergen specific to those antibodies enters the body, the mast cell releases histamines. Histamines dilate the blood vessels and fill the surrounding cells with fluid. This brings the onset of many symptoms including hives, itchy body, eyes and nose, wheezing, nausea, diarrhea and vomiting [5].
The non-mast cell histamine within the brain is much more complex, refer to Figure 3. As well as having a role in arousal, cognitive functions, and hormone secretion the histamine systems play a part in neurological and psychiatric disease [4]. Alzheimer's and Tourette Syndrome patients have been found to have lower levels of histamine where Parkinson's and schizophrenic patients have been found to have high levels of histamine. The low histamine levels are known to be associated with the onset of convulsions and seizures. As seen in Tourette Syndrome, motor tics are less severe forms of convulsions and seizures [4].
MAST CELL HISTAMINES |
NON-MAST CELL HISTAMINES |
REFERENCES
1 "What are enzymes?" Novozymes: Rethink Tomorrow. Retrieved 12 Feb 2014 http://www.novozymes.com/en/about-us/our-business/what-are-enzymes/pages/default.aspx#areproteins
2 "Histidine Decarboxylase" Wikipedia: The Free Encyclopedia. Retrieved 12 Feb 2014 http://en.wikipedia.org/wiki/Histidine_decarboxylase
3 "What is Histamine?" News Medical. Retrieved 12 Feb 2014 http://www.news-medical.net/health/What-is-Histamine.aspx
4 "Histamine in neurotransmission and brain diseases" PubMed.gov. Retrieved 12 Feb 2014 http://www.ncbi.nlm.nih.gov/pubmed/21713693
5 "How Allergies Work" How Stuff Words. Retrieved 12 Feb 2014 http://science.howstuffworks.com/life/human-biology/allergy2.htm
6 "Histidine Decarboxylase (HDC)" Uscn: Life Science Inc. Retrieved 12 Feb 2014 http://www.uscnk.com/directory/Histidine-Decarboxylase(HDC)-6476.htm
1 "What are enzymes?" Novozymes: Rethink Tomorrow. Retrieved 12 Feb 2014 http://www.novozymes.com/en/about-us/our-business/what-are-enzymes/pages/default.aspx#areproteins
2 "Histidine Decarboxylase" Wikipedia: The Free Encyclopedia. Retrieved 12 Feb 2014 http://en.wikipedia.org/wiki/Histidine_decarboxylase
3 "What is Histamine?" News Medical. Retrieved 12 Feb 2014 http://www.news-medical.net/health/What-is-Histamine.aspx
4 "Histamine in neurotransmission and brain diseases" PubMed.gov. Retrieved 12 Feb 2014 http://www.ncbi.nlm.nih.gov/pubmed/21713693
5 "How Allergies Work" How Stuff Words. Retrieved 12 Feb 2014 http://science.howstuffworks.com/life/human-biology/allergy2.htm
6 "Histidine Decarboxylase (HDC)" Uscn: Life Science Inc. Retrieved 12 Feb 2014 http://www.uscnk.com/directory/Histidine-Decarboxylase(HDC)-6476.htm
University of Wisconsin – Madison
Spring 2014 Genetics 564 |
TOURETTE SYNDROME |