One of the main characteristics of enzymes is their high specificity. A few enzymes exhibit absolute specificity; that is, they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. A complementary fit between the substrate and enzyme accounts for enzyme specificity. In addition non-covalent interactions between substrate and active site contributes to this spcificity. Thus complementary shape, charge and hydrophilic/hydrophobic characteristics of enzymes and substrates are responsible for the specificity of enzyme action.