This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
All of the following statements are true, EXCEPT: 
Select and explain. 
A. Cycloxygenase I is an inducible enzyme, B. Cycloyegenase II is induced by cytokines at sites of inflammation, C. PG's and leukotrienes are derived from arachidonic acid, D. Leukotrienes cause smooth muscle constriction
A: Cycloxygenase I is an inducible enzyme
Answer: A: Cycloxygenase I is an inducible enzyme 
Explanation: Cycloxgenase enzyme exist in two isoforms COX 1 and COX2. Cycloxygenase 1 is not an inducible enzyme, it has physiological house keeping functions. Cycloxygenase 2 is normally present only in minute quantities. It is an inducible enzyme, it is induced by cytokines and other signal molecules at the site of inflammation leading to the generation of prostaglandins which mediate inflammatory changes. Ref: Essentials of Medical Pharmacology By KD Tripathi, 5th Edition, Page 168.