An Enzymatic Conversion of Lipoxygenase Products by a Hydroperoxide Lyase in Blue-Green Algae (Oscillatoria sp.)

Abstract

An enzyme has been isolated from blue-green algae Oscillatoria sp. which utilizes the product, 13-hydroperoxy-9,11-octadecadienoic acid (13-HPOD), of lipoxygenase for its substrate. This enzyme, termed hydroperoxide lyase, converts the conjugated diene 13-hydroperoxide of linoleic acid to 13-oxotrideca-9,11-dienoic acid. The sturcture of the latter has been determined by ultraviolet spectroscopy and mass spectrometry. 9-HPOD is not a substrate for this enzyme. The hydroperoxide lysase from Oscillatoria sp. has a maximum of activity at pH 6.4 and 30.degree. C. The moleuclar weight of the enzyme was estimated at 56,000. The enzyme was not inhibited by BW 755C, but was inhibited by molecules containing more than one hydroxyl group. Quercetin was found to be the best inhibitor of the enzyme activity. The purified hydroperoxide lyase from Oscillatoria sp. showed an apparent Km of 7.4 micromolar and a Vmax of 35 nanomoles per minute per milligram of protein for 13-HPOD. An enzymatic pathway for the biogeneis of oxodienoic acid from linoleic acid is proposed. This involves the sequential activity of lipoxygenase and hydroperoxide lyase enzymes.