This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzymes, Subject name: Biochemistry
Histidine decarboxylase is present in 
Select and explain. 
A. RBC's, B. Hea, C. Liver, D. Kidney
C: Liver
Answer: C: Liver 
Explanation: Histamine is formed from histidine by decarboxylation, catalyzed by histidine decarboxylase. The effects of histamine are summarised in Table 16.3. Smooth muscle contraction, enhanced vascular permeability, increased acid secretion are the impoant actions. So histamine causes fall in blood pressure. The major cells producing histamine are platelets, mast cells, and basophils. Ceain antigens such as penicillin will elicit IgE antibodies that are fixed on the mast cells. When the next dose of penicillin is injected, it reacts with the antibodies; and degranulation of mast cells takes place. Histamine and slow reacting substance (SRS) are released. This leads to peripheral vasodilatation, fall in blood pressure and anaphylaxis.