Lacks dipeptidase activity and is unable to hydrolyze cystinyl-bis-glycine, leukotriene D4 and the beta-lactam antibiotic imipenem. The absence of activity may be due to the inability of asparagine (instead of aspartate found in DPEP1/2) at position 359 to function as the acid/base catalyst and activate the nucleophilic water/hydroxide. A tyrosine (instead of histidine) at position 269 reduces affinity for the beta zinc and may cause substrate steric hindrance 