While there are a few exceptions (some RNA molecules can act as enzymes, called ribozymes), the vast majority of enzymes are proteins.

Here's why:

* Structure: Proteins have complex three-dimensional structures that allow them to form specific active sites. These active sites are where the enzyme binds to its substrate and facilitates a specific chemical reaction.

* Specificity: Proteins can be highly specific in their function, binding to only certain substrates and catalyzing specific reactions. This specificity is crucial for the precise regulation of biochemical processes within cells.

* Catalytic Activity: The amino acid sequence of a protein determines its shape and, therefore, its catalytic activity. The arrangement of amino acids in the active site allows for specific interactions with the substrate, promoting the formation of a transition state and lowering the activation energy of the reaction.

So, while other molecules can play roles in biochemical reactions, enzymes are predominantly made of proteins.