What are the major types of molecules that modulate enzyme reaction or activity?

There are two types of molecules that modulate enzyme reaction – Activators and Inhibitors. 

Activators are a type of regulatory molecule that increase the activity of an enzyme. Enzyme activators may include ions, small organic molecules, peptides, proteins, and lipids. 

Inhibitors are a type of regulatory molecule that decrease the activity of an enzyme. Many pharmacological drugs and poisons can be categorized as enzyme inhibitors. Inhibitors are further categorized into two types – reversible and non-reversible.