The enzyme known as amylase acts on a specific substrate which is starch. The chemical reaction of starch begins in the mouth as it begins to hydrolyze into maltose, a sugar. Amylase, as all other enzymes, are very specific. One reason is that their 3-dimensional shape has a particular active site that binds to a substrate based on the molecular shape, much like a key fits to a particular lock. Other factors that affect enzyme specificity are charge as well as the hydrophilic and hydrophobic characteristics of both enzyme and substrate.