The Biosynthesis of Δ9,12,15,18-Tetracosatetraenoic and of Δ6,9,12,15,18-Tetracosapentaenoic Acids by Rat Testes

Abstract

Abstract Two 24-carbon polyenes previously reported in rat testes have been isolated and characterized to be Δ9,12,15,18-tetracosatetraenoic and Δ6,9,12,15,18-tetracosapentaenoic acids. The compounds were separated and purified by gas-liquid chromatography, and their structures were established by use of gas-liquid chromatography before and after hydrogenation, by ultraviolet spectroscopy of the alkaline isomerized derivatives, and by identification of fragments resulting from cleavage at double bonds by oxidative and reductive ozonolyses. The biosynthesis of the 24-carbon polyenes was studied after intratesticular injections of either 1-14C-linoleate or 1-14C-arachidonate. The two metabolic products, individually, were cleaved by oxidative ozonolysis, and the location of the 14C in the molecule was determined by gas-liquid radiochromatography of the fragments. The distribution of the 14C was consistent with the hypothesis that the 24-carbon polyenoic acids were biosynthesized by elongation and further desaturation of linoleic acid. Final proof was obtained by chemical carbon by carbon degradation and measurement of the specific activity of individual carbon atoms. After 1-14C-linoleate injection, Δ6,9,12,15,18-tetracosapentaenoic acid from testicular tissue was labeled primarily in the 7th carbon. After 1-14C-arachidonate injection, testicular Δ9,12,15,18-tetracosatetraenoate was labeled primarily in the 5th carbon. The suggested pathway of biosynthesis of the 24-carbon tetraenoic and pentaenoic acids is by a 2-carbon elongation of docosatetraenoic and of docosapentaenoic acids, respectively.