Here's why:

* Enzymes are biological catalysts: They speed up chemical reactions in living organisms without being consumed in the process.

* Proteins are complex molecules: They are made up of long chains of amino acids linked together by peptide bonds.

* Protein structure is essential for function: The specific sequence and folding of amino acids in a protein determine its shape and, crucially, its function.

* Enzymes have active sites: These are specialized regions on the enzyme's surface where the substrate (the molecule being acted upon) binds. The enzyme's shape and chemical properties allow it to interact with the substrate and facilitate the chemical reaction.

While other macro molecules like carbohydrates, lipids, and nucleic acids play vital roles in living organisms, enzymes are exclusively proteins.