Arachidonate 12-lipoxygenase (12-LO) from porcine leukocytes was expressed in insect cells using a baculovirus expression vector. The recombinant 12-LO was expressed as an N-terminal fusion protein with a 31-amino acid polypeptide carrying a six-histidine tag and an enterokinase cleavage site. Maximal intracellular enzyme activity and protein levels were observed 48 h after infection of Spodoptera frugiperda cells with the recombinant virus. Cells were lysed and the recombinant protein was purified in a single step by Ni2+-nitrilotriacetate column chromatography. The purified enzyme migrated as a single band on sodium dodecyl sulfate-polyacryl-amide gel electrophoresis. Recombinant enzyme catalyzed the formation of 12-hydroperoxy-5,8,10,14-eicosatetranoic acid and a small amount of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid. Chiral-phase HPLC analysis indicated that the 12-(S) enantiomer was the predominant product. The purified recombinant 12-lipoxygenase oxygenated linoleic acid to about 19% of the extent of oxygenation of arachidonic acid. Nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid inhibited the recombinant enzyme with IC50's of 2.2 and 0.06 micM, respectively. Expression of cloned porcine leukocyte 12-LO in S. frugiperda cells and purification by Ni2+-nitrilotriacetate chromatography provides a straightforward method for isolation of milligram quantities of this form of 12-LO.