Question

Why are substrate analogs used to monitor enzyme activity?

Can you please explain how this works and what the advantages are? Thank you!

Answer 1

Substrate analogs (substrate state analogues), are chemical compounds with a chemical structure that resemble the substrate molecule in an enzyme-catalyzed chemical reaction. Substrate analogs can act as competitive inhibitors of an enzymatic reaction. An example is phosphoramidate to the Tetrahymena group I ribozyme.

As a competitive inhibitor, substrate analogs occupy the same binding site as its analog, and decrease the intended substrate’s efficiency. The Vmax remains the same while the intended substrate’s affinity is decreased. This means that less of the intended substrate will bind to the enzyme, resulting in less product being formed. In addition, the substrate analog may also be missing chemical components that allow the enzyme to go through with its reaction. This also causes the amount of product created to decrease.

The binding of a substrate analog can stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalyzing its reaction. Substrate analog binding is either reversible or irreversible. Irreversible inhibitors usually react with the enzyme and change it chemically (e.g. via covalent bond formation). These inhibitors modify key amino acid residues needed for enzymatic activity. In contrast, reversible substrate analog  bind non-covalently and different types of analog are produced depending on whether these analog bind to the enzyme, the enzyme-substrate complex, or both.