DELTA-5 DESATURASE ACTIVITY IN RAT-KIDNEY MICROSOMES

Rat kidney microsomal fraction is able to catalyze the enzymatic desat uration of eicosatrienoic acid (20:3n-6) to arachidonic acid (20:4n-6) by the Delta 5 desaturase pathway, in the presence of reduced nicotin amide adenine dinucleotide (NADH), adenosinetriphosphate (ATP) and coe nzyme A (CoA). The substrate of the reaction [1-C-14] eicosa-8,11,14-t rienoic acid (20:3n-6), was separated from the product [1-C-14] eicosa -5,8,11,14-tetraenoic acid (20:4n-6) by reverse phase high-pressure li quid chromatography (RP-HPLC). These fatty acids were individually col lected by monitoring the eluent at 205 nm and their radioactivity was measured by liquid scintillation counting. The Delta 5 desaturase acti vity in kidney microsomes increased linearly with the substrate concen tration up to 20 mu M. 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 mu M and 60 p moles min(-1).mg(-1) microsomal protein, respectively. Neither the cyt osolic renal fraction nor the cytosolic liver fraction enhanced the De lta 5 desaturase activity. Contrary to a report but in accordance to o thers, the present results suggest that rat kidneys can synthesize ara chidonic acid at least to satisfy partially their needs for eicosanoid production.