The Enzyme Hexokinase Catalyzes the Addition of a Phosphate Group

The enzyme hexokinase catalyzes the addition of a phosphate group (taken from ATP) to a glucose molecule. Magnesium (Mg⁺⁺) , which is required for hexokinase to function properly, interacts with the ATP to facilitate binding to the hexokinase active site. Magnesium is therefore a(n) ____.

A) product
B) reactant
C) cofactor
D) substrate
E) enzyme