Kinetic Studies With Crude wild pear Lipoxygenase at during ripening and after storage

Abstract

Crude wild pear lipoxygenase (LOX) from ripe Kurdistan wild pears was used in this study. Extracted crude LOX was assayed spectrophotometrically for raw, ripe wild pear lipoxygenase and after 7-day storage. The effects of different buffers and pHs, substrate preparations, temperature, inhibitors and metal ions on LOX activity were evaluated at three conditions. The enzyme was most active with Hcl-Tris buffer at a pH of 7.5 and a temperature of 40oC. The best substrate was the first preparation with linoleic acid/Tween 20 at a ratio of 1:1. The kinetic parameters determined under the best conditions were a Km of 6.5 mM and a Vmax of 0.9 unit/mg protein for raw condition, 5.8 mM and a Vmax of 0.95 unit/mg protein for ripe condition and 5 mM and a Vmax of 1.1 unit/mg protein obtained after storage. The enzyme was heat-labile. It was shown that crude wild pear LOX is fully active at room temperature (20-30oC), while the best activity occurred at 35oC for Lox after storage that activity of lipoxygenase increased up to 130%. The results showed that lipoxygenase inhibitory activity of chemical compounds and standard compound decreased in the order of ascorbic acid > nicotinic acid > benzoic acid > DL-α-tocopherol. Monovalent and trivalent ions are inhibitors of LOX and divalent ions except Zncl2 are activators of LOX.