Two types of 15-lipoxygenase (15-LO) have been discovered and characterized, both of which metabolize arachidonic acid (AA) to produce 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE). 15-LO-1 oxygenates AA at both C-15 and C-12, whereas 15-LO-2 exclusively oxygenates C-15 of AA.{11792,4675} Human 15-LO-2 has a molecular mass of approximately 76 kDa and exhibits approximately 40% identity to the reticulocyte 15-LO-1.{4675,11789} Expression of 15-LO-2 appears to be restricted to prostate, lung, skin, and cornea and may play a role in the normal development of these tissues.{11790} The protein levels and enzymatic activity of 15-LO-2 are both down-regulated in prostate cancer compared with normal and benign prostate tissues, implicating a possible protective role for 15-LO-2 against tumor formation.{11790,8774,9075} Cayman's 15-LO-2 (human, recombinant) is expressed and purified from E. coli. The purity was determined using gel electrophoresis followed by coomassie staining. 15-LO-2 specific activity was established using arachidonic acid as the substrate and monitoring diene formation by measuring absorbance 236 nm.