Co-oxidation of acrylonitrile by soybean lipoxygenase and partially purified human lung lipoxygenase

Abstract

1. Human lung lipoxygenase (HLLO) was partially purified by concanavalin-A (ConA) affinity chromatography that provided an easy and rapid one-step procedure for the removal (⩾ 96%) of haemoglobin from cytosol. 2. HLLO exhibited dioxygenase activity towards arachidonic acid (AA) and linoleic acid (LA). The dioxygenase activity towards LA varied ∼ 12-fold (48-591 nmol/min /mg protein) among different human lung samples examined. 3. Reverse-phase HPLC analysis of AA metabolites indicated the predominance of 15-lipoxygenase in human lung cytosol. 4. HLLO exhibited co-oxidase activity towards benzidine (BZD) and several other model compounds. The co-oxidase activity towards BZD was significantly inhibited by several lipoxygenase inhibitors. 5. HLLO and soybean lipoxygenase (SLO), used as a model enzyme, metabolized acrylonitrile (ACN) to 2-cyanoethylene oxide (CEO) and ultimately to cyanide. 6. HLLO was a ∼ 6-fold better catalyst than SLO in converting ACN to cyanide. The generation of cyanide by HLLO was dependent on the concentration of enzyme and the reaction was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the anti-oxidant butylated hydroxytoluene (BHT). 7. Under optimal assay conditions, the covalent binding of HLLO-generated reactive intermediate(s) from [¹⁴C]ACN to protein and DNA (nmol equivalent bound/15/min mg/HLLO/mg bovine serum albumin or calf thymus DNA) was observed at ∼ 1.20 ± 0.13 and 2.20 ± 0.50 respectively. Both protein and DNA binding were inhibited by NDGA, butylated hydroxyanisole (BHA) and BHT.