Glycerolipid Composition of the Red Macroalga <i>Agarophyton Chilensis</i> and Comparison to the Closely Related <i>Agarophyton Vermiculophyllum</i> Producing Different Types of Eicosanoids

The red macroalga <i>Agarophyton chilensis</i> is a well-known producer of eicosanoids such as hydroxyeicosatetraenoic acids, but the alga produces almost no prostaglandins, unlike the closely related <i>A. vermiculophyllum</i>. This indicates that the related two algae would have different enzyme systems or substrate composition. To carry out more in-depth discussions on the metabolic pathway of eicosanoids between the two algae, we investigated the characteristics of glycerolipids, which are the substrates of eicosanoids production, of <i>A. chilensis</i> and compared them to the reported values of <i>A. vermiculophyllum</i>. In <i>A. chilensis</i>, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylcholine (PC) were the major lipid classes and accounted for 44.4% of the total lipid extract. The predominant fatty acids were arachidonic acid (20:4n-6), an eicosanoids precursor, and palmitic acid (16:0). The 20:4n-6 content was extremely high in MGDG and PC (&gt;70%), and the 16:0 content was extremely high in DGDG and SQDG (&gt;40%). A chiral-phase HPLC analysis showed that fatty acids were esterified at the <i>sn</i>-1 and <i>sn</i>-2 positions of those lipids. The glycerolipid molecular species were determined by reversed-phase HPLC&#8315;ESI&#8315;MS analysis. The main glycerolipid molecular species were 20:4n-6/20:4n-6 (<i>sn</i>-1/<i>sn</i>-2) for MGDG (63.8%) and PC (48.2%), 20:4n-6/16:0 for DGDG (71.1%) and SQDG (29.4%). These lipid characteristics of <i>A. chilensis</i> were almost the same as those of <i>A. vermiculophyllum</i>. Hence, the differences of the eicosanoids producing ability between the two algae would not be due to the difference of substrate composition but the difference of enzyme system.