Fatty acids of unusual double-bond positions and chain lengths found in rat skin surface lipids.

The fatty acids of rat skin surface lipids comprise four main skeletal types of chains which occur both as saturates and monoenes and range from C(12) to C(38): straight even, straight odd, iso and anteiso (the latter two identified by GC retention data only). Two unidentified series of branched monoenes also occur in trace amounts.Reductive ozonolysis of monoenes reveals two characteristic double-bond position patterns, one for the straight even chain series and the other for the straight odd chain series. The straight even chain pattern comprises four series, of which omega7 >>omega9>omega5>omega11; the straight odd chain series in contrast shows a large number of omega series with irregular distribution. The biosynthesis of the even chain fatty acid monoenes can be thought of as occurring in two stages: synthesis of 14ratioDelta9, 16ratioDelta9, 18ratioDelta9 and 20ratioDelta9, with 16ratioDelta9 predominating; elongation of these chains mostly by 1, 2, or 3 C(2) units but up to the unusually long lengths by 11 C(2) units. For the formation of the former, two schemes by known pathways are proposed.Iso and anteiso chains which are nearly all saturated comprised 1/3 the total fatty acids.