Two isoforms of lipoxygenase from mature grains of pearl millet [Pennisetum glaucum (L.) R. Br.]: purification and physico-chemico-kinetic characterization.

This study describes the partial purification and characterization of lipoxygenase (LOX) from pearl millet mature grains of inbred HBL 0843-2. Two isoforms of LOX, i.e., LOX 1 and LOX 2, were purified using ammonium sulphate fractionation, gel filtration chromatography and ion exchange chromatography near homogeneity to 56 and 40 folds with yield of 28 and 24%, respectively. LOX 1 and LOX 2 having molecular masses of approximately 85 and 79 kDa, respectively were purified. LOX 1 and LOX 2 exhibited maximum activity at pH 4.5 and 4.8, respectively at 25 °C temperature. Both the isoforms, which showed thermostability up to 35 °C when incubated for 30 min, were stable at a pH range of 7-7.8. LOX 1 and LOX 2 had apparent Km value of 0.86 and 0.57 µM, respectively. Ascorbic acid and vitamin E inhibited 66-78 and 61-69% activity of LOX 1 and LOX 2, respectively but Na+, Zn2+ and K+ strongly inhibited the activity of these isozymes. The present information about lipoxygenase enzyme might be valuable in drafting the strategies for its inactivation, which in turn can obstruct the LOX damaging effects on food products during processing and storage.