The purification of the microsomal fatty acid chain elongating system from beef adrenal cortex is described. The elongation system requires for optimal activity malonyl CoA, ATP, Mg2+, NADPH or NADH. Long chain fatty acyl CoA derivatives inhibit the incorporation of [1,3 14C]malonyl CoA into fatty acids. Supplementation of the system with enzymes of the C 3 oxidation sequence allows also an acetyl CoA dependent chain elongation. Microsomes from beef adrenal cortex contain 2,3 trans hexenoyl CoA reductase with similar properties as described for rat liver. The ratio of the specific activities of the hexenoyl CoA reductase and chain elongation remains constant in the course of purification from rat liver and beef adrenal cortex. From this finding it is concluded that hexenoyl CoA reductase is an integrated part of the microsomal malonyl CoA dependent chain elongation system. The physiological substrates of hexenoyl CoA reductase are 2,3 unsaturated acyl CoA derivatives of polyenoic long chain fatty acids with a preference for structures present in γ linolenic acid. Competitive inhibition of the microsomal enoyl CoA reductase by malonyl CoA with respect to enoyl CoA suggests that a multienzyme complex is involved in the microsomal chain elongation process. Octenoyl CoA, octenoyl pantethein and octenoyl acyl carrier protein are substrates of the microsomal hexenoyl CoA reductase from rat liver with decreasing maximal velocities and affinities. Octenoyl acyl carrier protein and malonyl CoA are competitive, suggesting identical mechanisms of reduction for octenoyl acyl carrier protein and octenoyl CoA by the multienzyme complex.
|Original language||English (US)|
|Number of pages||11|
|Journal||European Journal of Biochemistry|
|State||Published - Jun 1974|
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