Delta 5 desaturase activity in rat kidney microsomes.

Rat kidney microsomal fraction is able to catalyze the enzymatic desaturation of eicosatrienoic acid (20:3n-6) to arachidonic acid (20:4n-6) by the delta 5 desaturase pathway, in the presence of reduced nicotinamide adenine dinucleotide (NADH), adenosinetriphosphate (ATP) and coenzyme A (CoA). The substrate of the reaction [1-14C]eicosa-8,11,14-trienoic acid (20:3n-6), was separated from the product [1-14C]eicosa-5,8,11,14-tetraenoic acid (20:4n-6) by reverse phase high-pressure liquid chromatography (RP-HPLC). These fatty acids were individually collected by monitoring the eluent at 205 nm and their radioactivity was measured by liquid scintillation counting. The delta 5 desaturase activity in kidney microsomes increased linearly with the substrate concentration up to 20 microM. Enzymatic activity was sensitive to pH with the maximum at 7.0 and was proportional with incubation time up to 10 min. The apparent Km and Vmax of delta 5 desaturase were 56 microM and 60 pmoles.min-1.mg-1 microsomal protein, respectively. Neither the cytosolic renal fraction nor the cytosolic liver fraction enhanced the delta 5 desaturase activity. Contrary to a report but in accordance to others, the present results suggest that rat kidneys can synthesize arachidonic acid at least to satisfy partially their needs for eicosanoid production.

Occurrence of a 22∶2 nonmethylene interrupted dienoic fatty acid and its seasonal distribution among lipids and tissues of the fresh water bivalveDiplodon delodontus from an isolated environment.

Realatively high levels of a non-methylene-interrupted dienoic fatty acid were detected in the freshwater molluscDiplodon delodontus. The (7,13) 22∶2 NMID fatty acid was separated from total fatty acids by TLC, and its structure was determined by GLC and reductive ozonolysis. Its seasonal distribution was investigated in different tissues and lipids of the mollusc. High concentrations of this acid were found in polar lipids. The absence of the 22∶2 NMID fatty acid in the lipids of plankton and sediment in the same habitat suggests that it may be biosynthesized by themollusc. Possible synthesis and functions of the NMID fatty acids are discussed.