Depletion of Delta 9 desaturase (EC 1.14.99.5) activity in lactating rat during protein restriction

The effects of protein restriction on the activity of Delta 9 desaturase (E C 1.14.99.5) were investigated in lactating rats. A control group was fed a balanced diet (20% casein) for 14 days, whereas the experimental groups we re fed a low-protein diet (8% casein), supplemented with or without L-methi onine (0.4%), for 14 days. The enzyme activity was measured by incubations of hepatic microsomal pellets with (1-C-14) stearic acid. Results showed a decreased Delta 9 desaturase activity, after 2,7 and 14 days of depleted di et, of -50, -40 and -33% respectively, compared with control, The supplemen tation of the low-protein diet with 0.4% methionine, which favours food con sumption as well as growth, did not improve the altered Delta 9 desaturase activity. Our data evidenced that Delta 9 desaturase activity is depleted b y protein restriction during lactation, when the protein needs are high for the biosynthesis of animal tissues, This change has to be considered as a sign of depressed Delta 9 desaturase biosynthesis or modifications of enzym atic properties, or both. (C) 2000 Harcourt Publishers Ltd.