Here's why:

* Catalytic Activity: Proteins are incredibly versatile molecules with diverse shapes and chemical properties. This allows them to act as catalysts, speeding up biochemical reactions without being consumed in the process. This is the primary function of enzymes.

* Active Sites: Enzymes contain specific regions called active sites, where substrates bind and reactions occur. These active sites are often formed by the unique three-dimensional structure of the protein.

* Specificity: Proteins can be highly specific for their substrates, ensuring that the correct reactions occur at the right time and place.

* Regulation: Enzymes can be regulated, meaning their activity can be turned on or off, or their activity can be fine-tuned. This allows cells to control their metabolism and respond to changing conditions.

However, there are a few exceptions to this general rule:

* Ribozymes: Some enzymes are made of RNA, not protein. These are called ribozymes, and they are involved in processes like protein synthesis.

* Metalloenzymes: Some enzymes require non-protein components (cofactors) to function. These cofactors can be metal ions, organic molecules, or even other proteins.

Therefore, while most enzymes are predominantly protein-based, there are some exceptions that highlight the diverse nature of biological catalysis.