These enzymes catalyse the hydrolysis of various bonds. Some of these enzymes pose problems because they have a very wide specificity, and it is not easy to decide if two preparations described by different authors are the same, or if they should be listed under different entries. While the systematic name always includes 'hydrolase', the common name is, in most cases, formed by the name of the substrate with the suffix -ase. It is understood that the name of the substrate with this suffix, and no other indicator, means a hydrolytic enzyme. It should be noted that enzymes in EC 3.4 (peptidases) have recommended names rather than common names.