Final answer:
Enzymes are not one of the four major classes of organic compounds; they are a subset of proteins, which are one of the four main types of macromolecules.
Step-by-step explanation:
The question asks which of the following is not one of the four major classes of organic compounds. The four main types of macromolecules found in living organisms are proteins, carbohydrates, lipids, and nucleic acids. Therefore, the answer to the question is 'enzymes' because enzymes, while they are proteins, are not a distinct class of macromolecules; they are a subset of the proteins.