Stearyl CoA desaturation

JoshL V.C. Aranda, L.P. (1979). Hormonal regulation of the termiruil enzyme of microsomal stearyl CoA desatur[Pg.245]

We also checked the effect of catalase on Me since a recent report of Baker et al, (1976) has shown that this enzyme enhances the stearyl-CoA desaturation. For this reason the catalase activity of Sp, Cytosol and other fractions tested in the reactivation of Me were measured. Sp and the cytosol have catalase activity but the last one was relatively more active than the first one. Fig. 3 shows the comparative reactivation capacity of Sp, cytosol, DEAE Cellulose fraction and pure catalase on A6 desaturation and the content of units of catalase of each fraction. Results demonstrate that there is no correlation between the Sp reactivation capacity of a6 desaturation reaction and their catalase activity content. 

The fatty acid desaturase system was one of the first microsomal enzymes for which a lipid requirement was established. Using Fleischer s procedure of aqueous acetone extraction (Lester Fleischer, 1961) we were able to reduce the desaturase activity of hen liver microsomes to very low levels and restore activity completely with a mixture of lipids isolated from the microsomes (Holloway Peluffo, 1964 Jones at al., 1969). Shortly after this observation cytochrome bs was implicated in the desaturation process (Oshino et al., 1966). Progress in the isolation and purification of the stearyl CoA desaturase has been slow and it is only in the last two years that the complete resolution and reconstitution of the stearyl CoA desaturase has been achieved by Strittmatter and co-workers (Strittmatter et al., 1974). 

Many studies have revealed that thyroid hormones markedly affect lipid metabolism in man and in several species of animals. Concerning fatty acid biosynthesis it was demonstrated that the administration of thyroxine stimulates the incorporation of l-l c acetate into fatty acids in rats and mice (Dayton et al, I960) (Gompertz and Greenbaum, 1966) (March and Mayer, 1959). According to Gompertz and Greenbaum (1966) these observations appear to be associated with an increase of stearyl-CoA desaturase activity. Moreover Myant and Iliffe (1963) found that rats treated with thyroxine showed an inhibition of acetate incorporation, but not of malonate incorporation, into fatty acids by mitochondria free, subcellular liver preparations. Other authors have shown that the thyrotoxic state was accompanied by an increased incorporation of acetyl-CoA to fatty acid and a rise in the activity of fatty acid synthetase in rat livers (Diamant et al, 1972) (Roncari and Murthy, 1975). However, in vitro studies of fatty acid synthesis in which liver supernatant of 105,000 xg and microsomal preparations were incubated with the hormone showed that thyroxine inhibits de novo synthesis of palmitate and stimulates the desaturation reactions (Faas et al, 1972). 

In order to study the processes of plant fatty acid desaturation and glycerolipid biosynthesis and to develop a crop seed oil with reduced level of saturated fatty acids, a rat liver stearyl-CoA A-9 desaturase (D9DS) gene was introduced into Nicotiana tahacum under the control of the 35S promoter via Agrobacterium transformation (3) and soybean somatic embryos with the seed-specific phaseolin promoter by particle bombardment. In this article, we decribe the effects of the mammalian A-9 desaturase on fatty acid composition of membrane and storage lipids. 

All plant extracts that synthesize fatty acids from acetyl-CoA and mal-onyl-CoA are completely dependent upon the presence of ACP (Stumpf, 1977 Ohlrogge et al., 1979). In addition, its role as the thioester component of the primary elongation substrate, namely, palmityl-ACP, and the first desaturation substrate, stearyl-ACP, is well documented (Jaworski and Stumpf, 1974 Jaworski et al., 1974). Two plant ACPs have been isolated and characterized, one from avocado mesocarp and one from spinach leaves (Simon et al., 1967). The characteristics of these ACPs, as compared to prokaryotic ACPs, are given in Table I. 

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