What is the missing reagent in the reaction below? 
Definitions:
Parathyroid Hormone
A hormone secreted by the parathyroid glands that regulates calcium levels in a person's body.
Blood Calcium Levels
The concentration of calcium in the blood, crucial for various physiological processes including bone formation and muscle contraction.
Amino Acid Derivatives
Simplest hormones, such as epinephrine and melatonin, that are derived from amino acids.
Fatty Acid Derivatives
Prostaglandins, juvenile hormones of insects, and other compounds derived from fatty acids.
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