The material on which an enzyme acts. Enzymes are biological catalysts that speed up biochemical reactions and catalyze the conversion of substrate molecules into product molecules.
When the biological functions of an enzyme are not known, one way to discover an enzyme’s function is to determine its substrate specificity, which are the particular proteins and small molecules that act as substrates to the enzyme. These substrates are recognized and bound by catalytic cavities called active sites on the enzyme. Determination of substrates is a step towards creating molecules that may inhibit enzymes. Drugs that inhibit the activity of certain enzymes can be substrate analogs or mimics that may competitively bind the active site.