Structural importance of the cis ‐5 ethylenic bond in the endogenous desaturation product of dietary elaidic acid, cis ‐5, trans ‐9 18∶2 acid, for the acylation of rat mitochondria phosphatidylinositol

When rats were fed elaidic ( trans ‐9 18∶1) acid at a high load in diets that were otherwise marginally or almost completely deficient in linoleic ( cis ‐9, cis ‐12 18∶2) acid, elaidic acid was desaturated to cis ‐5, trans ‐9 18∶2 acid. This polymethylene‐interrupted acid was then incorporated into most phospholipids from rat mitochondria, cardiolipin being an exception. Its level of esterification in phospholipids followed the increasing order: phosphatidylethanolamine kidney > heart. The levels of cis ‐5, trans ‐9 18∶2 acid increased in mitochondria phospholipids as the level of linoleic acid was lowered in the diet. In liver mitochondria PI, it reached 16% of total fatty acids. After hydrolysis of liver mitochondria PI with Naja naja phospholipase A 2 , we observed that elaidic acid was essentially esterified to position 1 at the expense of saturated acids, whereas cis ‐5, trans ‐9 18∶2 acid was exclusively esterified to position 2, along with 20∶3n−9 and 20∶4n−6 acids. As a consequence, the sums of saturated and trans ‐9 18∶1 acids on the one hand, and of 20∶3n−9, 20∶4n−6, and cis ‐5, trans ‐9 18:2 acids on the other hand, remained fairly constant in liver mitochondria PI (ca. 55 and 30%, respectively). Because trans ‐9 18∶1 and cis ‐5, trans ‐9 18∶2 acids differ only by the cis ‐5 ethylenic bond, which is also present in 20∶3n−9 and 20∶4n−6 acids, this distribution pattern indicates that the cis ‐5 double bond, rather than any other ethylenic bond, may be of major structural importance for channeling fatty acids to position 2 of PI.