This invention provides amidases, polynucleotides encoding the amidases, methods of making and using these polynucleotides and polypeptides. In one aspect, the invention provides enzymes having secondary amidase activity, e.g., having activity in the hydrolysis of amides, including enzymes having peptidase, protease and/or hydantoinase activity. In alternative aspects, the enzymes of the invention can be used to used to increase flavor in food (e.g., enzyme ripened cheese), promote bacterial and fungal killing, modify and de-protect fine chemical intermediates, synthesize peptide bonds, carry out chiral resolutions, hydrolyze Cephalosporin C. The enzymes of the invention can be used to generate 7-aminocephalosporanic acid (7-ACA) and semi-synthetic cephalosporin antibiotics, including caphalothin, cephaloridine and cefuroxime. The enzymes of the invention can be used as antimicrobial agents, e.g., as cell wall hydrolytic agents. The invention also provides a fluorescent amidase substrate comprising 7-(.epsilon.-D-2-aminoadipoyladipoylamido)-4-methylcoumarin.