cofactor is a non-protein
chemical compound that is bound (either tightly or loosely) to an enzyme and is required for catalysis.
They can be considered "helper molecules/ions"
that assist in biochemical transformations. Certain substances such as water
and various abundant ions may be bound tightly by enzymes,
but are not considered to be cofactors since they are ubiquitous and rarely
limiting. Some sources limit the use of the term "cofactor" to