DEPLETION OF DELTA-9 DESATURASE (EC-1.14.99.5) ENZYME-ACTIVITY IN GROWING RAT DURING DIETARY-PROTEIN RESTRICTION

The effects of protein restriction on DELTA9 desaturase (EC 1 . 14.99.5) activity were studied in growing rats. A control group was fed on a balanced diet (200 g casein/kg; BD) for 28 d. The experimental group was fed on the low-protein diet (20 g casein/kg; LP) for 26 d, then refed the balanced diet (BD-R) for 2 d. Rats were born to and suckled from normally fed dams. The enzyme activity was measured after 2 and 14 d of LP, and 26 d of LP plus 2 d of BD-R, by incubations in vitro of hepatic microsomal pellets with [1-C-14]stearic acid. The results indicated a decreased DELTA9 desaturase activity after 2 and 14 d of LP of - 33 and - 43 % respectively. Refeeding for 2 d was sufficient to super-repair this activity (+66 %). The fatty acid composition of total liver lipids and microsomal phosphatidylethanolamines (PE) and phosphatidylcholines (PC) were also investigated; 18:0 decreased in total liver lipids at 14 d of LP, when 18:1n - 9 increased. Stearic acid (18:0) increased in PC at 2 d of LP and in PE at 14 d of LP; oleic acid (18:1n - 9) did not change. Therefore, it is concluded that a defect occurred in the bioconversion of 18:0 into 18:1n - 9 by DELTA9 desaturation during protein depletion. As oleic acid is accumulated in total liver lipids during LP, we speculate that this is due to a decreased oxidation or transport of this fatty acid.