They can be found in all living organisms and play a key role in metabolic pathways. There are two categories of enzymatic reactions, called catalytic and non-catalytic. Catalytic reactions usually require the presence of an iron ion (Fe++) while non-catalytic reactions do not require Fe++ ions. Biotransformation enzymes are involved in the incorporation of drugs into their metabolites by use of active transport or shuttling mechanisms.

Enzymes are proteins, and their structures differ from those of other proteins because they have extra amino acids attached to the N-terminus of the polypeptide chain (the backbone). This extra material is known as the "active site," which contains an active site pocket where
one molecule binds to another with its covalent bond rather than through attraction between polar side chains such as those found in some non-enzymatic reactions like hydrogenation or hydration reactions.

Biotransformation enzymes are catalytic or non-catalytic. The term catalytic refers to the fact that they require the presence of an iron ion (Fe++) in order to occur, while non-catalytic reactions do not require this. In general, catalytic reactions are faster than non-catalytic ones because they involve more molecules interacting at once and therefore require less time for completion.