Fatty acid Δ5 desaturation in rat liver cell nuclei
- 24 Downloads
Activity of one of the key enzymes involved in arachidonic acid (20:4 n−6) biosynthesis, the Δ5 desaturase, was found in rat liver cell nuclei. Up to now, it has been shown that the fatty acid desaturases are located exclusively in the endoplasmic reticulum. Similarly to what happens with microsomal enzyme the nuclear Δ5 desaturase enzyme was only fully active in the presence of a cytosolic factor. In this condition it reached a specific activity of 50 pmol 20:4 n−6 formed/min/mg of protein. This fact would imply that purified nuclei like purified microsomes lack a soluble cytosol factor necessary for the total desaturation reaction expression. Besides the nuclear Δ5 desaturase has an optimal pH of 7.6 and is inhibited by 1 or 10 mM KCN. Low long chain acyl-CoA synthetase activity that catalyzes the formation of 20:3 n−6-CoA, was also found in liver nuclei. This step would be essential in nuclear desaturation since when ATP and/or CoA (necessary for the acylation reaction) are omitted from the incubation mixture, the desaturation reaction does not take place.
Key WordsΔ5 desaturase acyl-CoA synthetase nuclei fatty acid composition
Unable to display preview. Download preview PDF.
- 11.Burton K: Determination of DNA concentration with diphenylamine. Methods Enzymol 12: 163–166, 1969Google Scholar
- 13.Shephard EH, Hübscher G: Phosphatidate biosynthesis in mitochondrial subfractions of rat liver. Biochem J 118: 429–440, 1969Google Scholar
- 16.Porteous JW, Clark B: The isolation and characterization of subcellular components of the epithelial cells of rabbit small intestine. Biochem J 96: 159–171, 1975Google Scholar
- 19.Garda HA, Leikin AI, Brenner RR: Determination of fatty acid desaturase activities by RP-HPLC. An Asoc Quím Arg 80: 365–371, 1992Google Scholar
- 29.Fahl WE, Jeffcoat CR, Kasper CB: Characteristics of benzo(a) pyrene metabolism and cytochrome P450 heterogenity in rat liver nuclear envelope and comparison to microsomal membrane. J Biol Chem 253: 3106–3113, 1975Google Scholar
- 30.Matsuura S, Fujii-Kuriyama SY, Tashiro Y: Distribution and induction of cytochrome P450 in rat liver nuclear envelope. J Biol Chem 91:212–220, 1981Google Scholar