Why are enzymes macromolecules?

The possible reasons for the macromolecular nature of enzymes are discussed. They are recognized in the necessity of creating a highly specific stereochemistry and microenvironment in the active site, in the necessity of maintaining the protein conformational rigidity, its fit with the physiological environment and overall stability, in allostery, and in the possible existence of fossil sequences, molecular tinkering, and specific hydrodynamic properties.