The effect of soluble rat liver proteins on the activity of microsomal stearoyl-CoA and linoleoyl-CoA desaturase

Abstract

1. 1. The influence of bovine serum albumin and soluble rat liver proteins on the activity of rat liver microsomal Δ 9 and Δ 6 desaturases has been studied. 2. 2. In the absence of bovine serum albumin, the Δ 9 desaturase which converts stearoyl-CoA into oleoyl-CoA, shows a non-linear correlation between enzyme activity and protein concentration. 3. 3. Optimum concentrations of bovine serum albumin have three main effects on the enzyme activity: (i) establishes a linear relationship between enzyme activity and protein concentration, (ii) stimulates the enzyme activity 2–3 fold and (iii) raises the optimum substrate concentration from 10 to 100 μM. 4. 4. A highly purified soluble liver protein of molecular weight 24000 also stimulated the enzyme activity and brought about a linear relationship between enzyme activity and protein concentration. 5. 5. It was concluded that the non-linear kinetics were due to limiting amounts of substrate binding protein in the microsomal preparations. 6. 6. The Δ 6 desaturase which converts linoleoyl-CoA into γ-linolenoyl-CoA was also stimulated by bovine serum albumin and soluble liver proteins. 7. 7. The significance of the fatty acid-binding proteins is discussed.