EFFECT OF CERULENIN ON THE SYNTHESIS OF VERY-LONG-CHAIN FATTY-ACIDS IN MICROSOMES FROM LEEK SEEDLINGS

Cerulenin inhibits the elongation of stearoyl-CoA and eicosanoyl-CoA by microsomes from leek seedlings. The inhibition depends on the cerulenin concentration and affects the biosynthesis of docosanoic and tetracosanoic acids only slightly more than that of eicosanoic acid. A 30-min preincubation of the microsomes with cerulenin allows a quantitative inhibition of the elongation at 50 muM cerulenin (50% inhibition at 15 muM cerulenin). A kinetic study of the elongating activity in the presence or in the absence of the inhibitor suggests that the inhibition is non-competitive. Analysis of the products of the reaction suggests that 3-ketoacyl-CoA synthase is the target of cerulenin. A study of the partial reactions demonstrates that the inhibition affects almost exclusively the condensation step.