BphH is a divalent metal ion-dependent hydratase that catalyzes the forma-tion of 2-keto-4-hydroxypentanoate from 2-hydroxypent-2,4-dienoate (HPDA). This reaction lies on the catabolic pathway of numerous aromat-ics, including the significant environmental pollutant, polychlorinated biphenyls (PCBs). BphH from the PCB degrading bacterium,Burkholderia xenoveransLB400, was overexpressed and purified to homogeneity.