Biology-Today.com

There can be many optical isomers of a substrate. However, it is only one of the isomers which acts as a substrate for enzyme action eg.; for hydrolysis of poplypeptides at D- and L- amino acids- there are two types of enzyme needed which will act on D- and L- isomers of amino acids. Trypsin [...]

Enzymes are able to bind to other small molecules in the cell because the 3-D shape of the enzyme fits a small molecule to undergo a chemical reaction as a result. This molecule is called the substrate of that enzyme. A particular enzyme atcs on very specific molecule called the substrate and thus an enzyme [...]