Rapid Methods for Lipoxygenase Assay in Sweet Corn
Potential methods for rapid assay of sweet corn lipoxygenase (LPO) were evaluated and compared by visual inspection. Both model system (partially purified) and vegetable (LPO extract) system studies were carried out. Model system studies indicated that LPO had maximum activity at pH 6.0 and 2.0 mM linoleic acid. Methylene blue bleaching (MBB), carotene bleaching (CB), and potassium iodide-starch (KI-S) methods were evaluated both spectrophotometrically and visually. Both MBB and KI-S methods were effective for the model system. For the vegetable LPO extract systems (sweet corn and green beans), the MBB method indicated positive results for both, the CB method was not effective for either, and the KI-S method was very effective for green beans but not for sweet corn.
Partial Purification and Characterization of Asparagus Lipoxygenase
Lipoxygenase (LOX) from fresh asparagus was partially purified by extraction of acetone-washed asparagus powder with pH 4.5 potassium phosphate, ammonium sulfate fractionation and carboxymethyl-cellulose (CMC) chromatography. Asparagus LOX purified by ammonium sulfate fractionation had a pH activity optimum of 5.5–6.0 and was stable at pH 4.5–8.0 when stored at 2°C. Asparagus LOX was active on monolinolein as well as linoleic acid, but activity was very low on di- or tri-linolein. The CMC fractions with greatest LOX activity were nearly free of peroxidase activity while the protein fractions which did not bind with CMC at pH 5 were peroxidase active. The LOX activity in the purified asparagus extract was 90% inhibited by 1 mM cyanide when preincubated for 30 min at 25°C.
Soya-bean lipoxygenase: an iron-containing dioxygenase.
Abstract Metal analysis by atomic absorption indicated the presence of one atom of iron in soya-bean lipoxygenase (linoleate: oxygen oxidoreductase, EC 1.13.11.12). Preincubation of the enzyme at pH 9 with chelating agents resulted in substantial inhibition. The results may indicate a role for the iron atom in lipoxygenase action.