Substrate specificity and characterization of partially purified rat liver 13-hydroxyoctadecadienoic acid (13-HODE)...

Oxidation products of linoleic acid, such as 13-hydroxyoctadecadienoic acid (13-HODE), exhibit biological activity in a number of systems. One major metabolic fate of 13-HODE is oxidation to the 2,4-dienone, 13-oxooctadecadienoic acid by an NAD(+)-dependent dehydrogenase (13-HODE dehydrogenase). The present work describes the partial purification and characterization of 13-HODE dehydrogenase from rat liver cytosol. The enzyme was purified using a combination of ammonium sulfate precipitation, as well as hydroxylapatite, gel permeation, and hydrophobic interaction chromatography. Analysis of the most purified preparation by SDS-polyacrylamide gel electrophoresis indicates two subunits of approximately 55 kDa, suggesting the possibility of a heterodimeric enzyme. However, due to aggregation in the purified preparation, an accurate molecular mass for the native enzyme has not yet been obtained. Using 13-HODE as a substrate, the purified enzyme has a Km of 6.3 microM and a Vmax of 5.7 nmol/min/mg. More importantly, the enzyme has a narrow substrate specificity with 13-HODE being the preferred substrate. From a series of 17 potential substrates, only 9-HODE (53% the activity of 13-HODE) and 15-hydroxyeicosatetraenoic acid (64% the activity of 13-HODE) showed significant activity as substrates. A number of other unsaturated hydroxy fatty acids, including several eicosanoids, are not substrates. The narrow substrate specificity displayed by the enzyme suggests that it could play a key role in modulating the effects of oxidized derivatives of linoleic acid.