What occurs when the enzyme in an ELISA test is attached to a substrate?

When the enzyme in an ELISA test is attached to a substrate, it catalyzes a reaction that typically leads to a color change. This occurs because the enzyme acts on the substrate, which is usually a specific compound that the enzyme can convert into a different product. In many ELISA assays, the substrate is designed to produce a colored product when acted upon by the enzyme, which makes it possible to visualize and quantify the results of the assay. This color change serves as an indicator of the presence of the target molecule, often a protein or antigen, in the sample being tested.

Notably, the other options do not accurately describe the biochemical activity taking place during the enzyme-substrate interaction in an ELISA. For instance, the enzyme does not remain inactive; it becomes active upon binding to the appropriate substrate. A colorless dye is typically an intermediate or the starting point in the process that requires the enzyme’s action to produce a colored product, affirming that the production of color is integral to the process. Additionally, while there are antibodies involved in the ELISA setup to capture or bind the target, the substrate does not bind with the antibody; rather, it interacts specifically with the enzyme linked to the antibody to produce the detectable signal.