Studies on the partial degradation of polyunsaturated fatty acids in rat-liver mitochondria.

Abstract

In rat liver some highly unsaturated fatty acids are partially degraded. In contrast to “normal”β‐oxidation some intermediates accumulate in this catabolic pathway. When a docosapolyenoic acid with the first double bond in position 4 is metabolized, two degradation products are to be found. The sequence of reactions has been elucidated. As a first step the docosapolyenoic acid loses its double bond in position 4 while the carbon chain remains unchanged. The enzyme involved has tentatively been called 4‐enoyl‐CoA reductase. Subsequently chain shortening occurs. Using polyenoic acids with different chain lengths and different double bond positions, it has been possible to demonstrate that the double bond positions rather than the chain length determine whether or not an unsaturated fatty acid is partially degraded. The four double bonds in the positions 4, 7, 10 and 13 seem to be the minimal structural requirement for docosapolyenoic acids in order to function as substrates for the 4‐enoyl‐CoA reductase. 4, 7, 10‐docosatrienoic, 4, 7‐docosadienoic, and 4‐docosenoic acid, which have not been detected in nature so far, are not metabolized when incubated with rat liver mitochondria.