Lipid metabolism of the yellow clam, Mesodesma mactroides: 2-polyunsaturated fatty acid metabolism.

The fate of labeled linoleic, alpha-linolenic, and higher homologs of alpha-linolenic acid administered to the yellow clam, Mesodesma mactroides, was investigated. It was found that the clam incorporated the acids dissolved in sea water and converted 18:2 (n-6) into 20:2 (n-6) and 18:3 (n-3) into 18:4 (n-3) and 20:3 (n-3). The addition of casein hydrolysate to the sea water increased the desaturation capacity of the calm and allowed the conversion of 18:2 (n-6) into 18:3 (n-6) to be demonstrated. An enhanced desaturation of 18:3 (n-3) into 18:4 (n-3) was also demonstrated. After 12 hr admininistration of the acid, no radioactivity was found in arachidonic, 20:5 (n-3), or 22:6 (n-3). Feeding the clams a culture of Phaeodactylun tricornutum previously incubated with 1-14C-alph-linolenic acid demonstrated that all the homologs of the alpha-linolenic series were found in the clam without any important changes. Six hour administration of labled linolenic acid resulted in the incorporation of the acid into diglycerides and phospholipids.