Acyl CoA elongases

Evidence that the acyl-CoA elongases regulate hydrocarbon chain length and pheromone production... 

The regulation of the chain length specificity to produce the specific blend of hydrocarbons often used in chemical communication appears to reside in the microsomal fatty acyl-CoA elongase reaction and not in the reductive conversion of fatty acyl-CoAs to hydrocarbon. The American cockroach produces three major hydrocarbons n-pentacosane, 3-methylpentacosane and (Z,Z)-9,12-heptacosadiene (Jackson, 1972). Studies with microsomes from integument tissue showed that stearyl-CoA was elongated up to a 26 carbon acyl-CoA that could serve as the precursor to n-pentacosane. In contrast, linoleoyl-CoA... 

Fehling, E. and Mukherjee, K.D. (1991) Acyl-CoA elongase from a higher plant Lunaria annua) metabolic intermediates of... 

Bessoule, J-J., Creach, A., Lessire, R. and Cassagne, C. (1992) Evaluation of the amount of acyl-CoA elongases in leek (Allium porrum L.) leaves. Biochim. Biophys. Acta 1117, 78-82. 

Fehling E., Lessire, R., Cassagne, C. and Mukherjee, K.D. (1992) Solubilization and partial purification of acyl-CoA elongase from Lunaria annua. Biochim. Biophys. Acta 1126, 88-94. 

It was shown years, ago that C20-C24 fatty acids are chiefly located in the plasma membrane of leek cells, but are synthesized in (by) the endomembrane system. Two acyl-CoA elongases were detected, one elongating ClS-CoA chiefly in the ER, the second elongating C20-CoA chiefly in the GA. The elongases were solubilized and partially purified. The kinetic parameters have been studied and the role of the surrounding membrane lipids on the C20-C24 fatty acid biosynthesis is being investigated (see also LESSIRE et al., this volume BESSOULE et al., this volume). 

TECHNIQUES FOR THE PURIFICATION OF ACYL-CoA ELONGASE FROM ALLIUM PORRUM LEAVES... 

The activity of the acyl-CoA elongase was studied at malonyl-CoA concentrations in the range of 1 to 200 and at a stearoyl-CoA concentration of 6.9 M. The double-reciprocal plots of Figure 3A shows the relationships between malonyl-CoA and/or stearoyl-CoA concentration and malonyl-CoA condensation to stearoyl-CoA.The apparent Km was 160 pM for the malonyl-CoA.The activity of the (at least partially restored) acyl-CoA elongase was studied at different concentrations of CI8-C0A (Figure 3B), in the presence of 13.2 pg of soybean PC vesicules and 4.6... 

TABLE 1 REACTION PRODUCTS OF THE PARTIALLY PURIFIED ACYL-CoA ELONGASE. 

As preliminary experiments, the influence of the addition of different amounts of lipids excluded from the DEAE-column ("leek lipids") on the CI8-C0A elongase activity was studied (Table 2). The phospholipid composition of the lipid extract was determined by TLC densitometry as 3.31, 0.86 and 0.35 pg for PC, PS and PE respectively. The role of PC was chiefly studied and the influence of the addition of soybean PC vesicles on CI8-C0A elongation was checked. In the presence of 19.8 pg of PC, the activity increased from 0.4 to 1.2 nmoles/mg/h. The highest activities were observed in the presence of 4.6 pg "leek lipids" with 13.2 pg of PC. Under these conditions the CI8-C0A elongation was increased 6.5-fold. These results indicated that the addition of PC alone, which was the predominant lipid in the microsomes, is not sufficient to completely restore the acyl-CoA elongase activity.The ad-... 

TABLE 2 INFLUENCE OF LIPIDS ON THE ACYL-CoA ELONGASE ACTIVITY. 

Acyl-CoA elongase activity was measured, using 1.5 pg of partially purified enzyme in the presence of different quantities of non-retained DEAE leek lipids and soy-bean PC. 

Owing to the nature of the substrates, it has been proposed that acyl-CoAs are attached by partly ionic, partly hydrophobic, interactions to the condensing enzyme, whereas the malonyl-CoA is attached chiefly by ionic interactions (1). The condensation creates a malonyl-CoA like structure which disappears progressively as the reaction proceeds, so that the chain under formation leaves the malonyl-CoA site for the acyl-CoA site after the dehydration. A study of the modulation of the activity of the acyl-CoA elongases requires that these properties be taken into account. 

What makes that an acyl-CoA elongase from Simmondsia chinensis forms only monounsaturated VLCFA whereas those from leek leaves form exclusively the saturated ones It has been postulated that this could result from either the specificity of the elongases towards saturated or unsaturated acyl-CoAs, or from the competition of other enzymes for the same substrates. The first hypothesis was ruled out in leek when it was demonstrated that the purified elongases had no specificity towards the acyl chain-length or the unsaturation (3). 

Bessoule JJ, Lessire R, Cassagne C. Partial purification of the acyl-CoA elongase of Allium porrum leaves. Arch Biochem Biophys 1989 268 475-484. 

Lessire R, Bessoule JJ, Cassagne C. Involvement of a 3-ketoacyl-CoA intermediate in acyl-CoA elongation by an acyl-CoA elongase purified from leek epidermal cells. Biochim Biophys Acta 1989 1006 35-40. 

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