Characterization of lipoxygenase activity from a partially purified enzymic extract from Morchella esculenta

A crude extract (FI) from Morchella esculenta was partially purified using ammonium sulphate precipitation at 0-60, 60-80 and 80-100% of saturation to obtain fractions (FIIa), (FIIb) and (FIIc), respectively. The highest specific lipoxygenase (LOX) activity was obtained in fraction (FIIa) which showed a recovery of 12.8% and a 2.5-fold increase in purification. Partially purified LOX extract exhibited optimal activity at the acidic pH of 3.0 and showed 62.5% of the maximal activity in the pH range of 4.0-6.0 and less than 12.5% activity in the pH range of 7.0-10.0. Kinetic studies indicated that the LOX activity of fraction (FIIa) had a V-max of 0.314 mu mol hydroperoxide mg protein(-1) min(-1) and a corresponding K-m value of 1.59 x 10(-4) M. The enzymic activity exhibited a strong specificity towards linoleic acid as substrate while only 29% activity was observed using linolenic acid and approximately 11% was obtained with mono-, di- and trilinolein: however, LOX activity showed a relatively strong affinity (83%) towards arachidonic acid as substrate. The enzymic activity of fraction (FIIa) catalyzed the bioconversion of linoleic acid at pH 6.0 into the corresponding 9-, 10-, 12- and 13-hydroperoxides at a ratio of 36:24:14:26, respectively. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.