Part 1. Definition
In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.
Part 2. Example
Inhibition of the human ether-a-go-go-related gene (HERG) potassium channel by cisapride: affinity for open and inactivated states. 
Answer: potassium
Explanation:  Potassium is a type of electrolyte mineral that helps our nerves to function and muscles to contract. Hence, it should be tagged as chemical.
Part 3. Exercise
Localization of an 11 beta hydroxysteroid dehydrogenase activity to the distal nephron. Evidence for the existence of two species of dehydrogenase in the rat kidney.
Answer:
11 beta hydroxysteroid