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 [...]

An enzyme may be defined as a protein with catalytic properties due to its power of specific activation. Like all catalysts enzymes have the property of reappearing essentially unchanged at the end of a reaction. Two striking features about enzymes make them best catalysts known. These are their effectiveness and their specificity.