(ii) highly specific in that they can distinguish between similar parts of the substrate molecule (regiospecificity), and between optical isomers of the substrate (streospecificity). In addition, enzymes

(iii) are subject to a variety of regulations, and

(iv) their reaction rates show substrate saturation, which is not the case with catalysts (nonbiological). Enzymes are attractive because

(v) they operate under mild conditions of temperature, pressure and pH, which save energy, and

(vi) undesirable by products are not produced by enzymes.