Existence of 5-Lipoxygenase in Ogonori, Gracilaria asiatica, and Its Inactivation by Cooking and Gastric Acid [in Japanese]

Junko Sajiki

Public Health Laboratory of Chiba Prefecture, 666-2 Nitona-cho, Chuo-ku, Chiba, 260-8715, Japan

An existence of 5-lipoxygenase in Gracilaria asiatica, a species of red algae causing deaths of three persons who ate cooked one in Japan, was confirmed using agonists and an antagonist. The involvement of the enzyme in food poisoning was also investigated. Leukotriene (LT)B₄, a stable metabolite of arachidonic acid (AA) catalyzed by 5-lipoxygenase, increased significantly in algae with putative stimuli, such as Ca ionophore A23187, Diamide and N-ethylmaleimide. The increase of LTB₄ by Diamide was inhibited significantly by AA861, a 5-lipoxygenase inhibitor. No change in concentrations of two isomers out of three, 6-trans-LTB4 and 6-trans-12-epi-LTB₄, was observed when these stimuli were added. The other naturally existing isomer which possesses the same molecular weight as LTB₄, but not identified stereochemically, showed a synchronized change with LTB₄. The 5-lipoxygenase activity was lost by boiling raw algae for 10 min or further incubating the heated algae for 1 h at 37℃ with 0.03 N HCl (pH 2). However, LTB₄ contents in the ethanol extracts from algae after these treatments increased significantly. These findings demonstrate that G. asiatica possesses an AA metabolic pathway via 5-lipoxygenase, but the enzyme activity would be lost by cooking, and also by ingesting in the stomach. The cortex of cooked algae would become soften in the stomach, resulting in the effective extraction of LTB₄from algae in situ.