The preferred metabolic pathway from linoleic acid to arachidonic acid in vitro

Abstract

1. 1. The two possible pathways which lead from linoleic acid to arachidonic acid were simultaneously studied in liver microsomes from fat-deficient rats and from fat-fed rats. 2. 2. The overall yields of the conversion of linoleic acid to eicosa-8,11,14-trienoic and arachidonic acids were calculated and gave a ratio of 16 to 1 for the pathway via γ-linolenic acid over the pathway via eicosa-11,14-dienoic acid in the fat-fed rat, and a ratio of 6 to 1 in the fat-deficient rat. 3. 3. The side reactions to the alternate pathways were also investigated. A relatively high rate of chain elongation was found for eicosa-8,11-dienoic acid which minimizes the importance of the pathway via this acid. 4. 4. The inhibition and enhancement of the different reactions in the two pathways were tested under the same conditions using either mixtures of fatty acids extracted from rat livers or single fatty acids of the linoleic acid family. 5. 5. The interactions of the different acids in chain elongation and desaturation reactions are of small magnitude. However, the desaturation of eicosa-8,11,14-trienoic acid is strongly enhanced by linoleic and γ-linolenic acids which may account for its non-accumulation in tissue lipids.