Fatty acyl-CoA elongase

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... 

This pathway (the microsomal system ) elongates saturated and unsaturated fatty acyl-CoAs (from Cjg upward) by two carbons, using malonyl-CoA as acetyl donor and NADPH as reductant, and is catalyzed by the microsomal fatty acid elongase system of enzymes (Figure 21-5). Elongation of stearyl-CoA in brain increases rapidly during myehnation in order to provide C22 and C24 fatty acids for sphingoEpids. 

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). 

Fatty acid elongation mainly occurs in the endoplasmic reticulum where elongases add two carbons to acyl-CoA substrates by using malonyl-CoA. Elongases are the rate-limiting protein acting in a multi proteic complex including a... 

Acyl-CoA synthetase activity is dependent on the presence of ATP, Mg, free fatty acid and CoASH. Therefore, we examined the effect of CoASH on elongase and acyl-CoA synthetase activities. In leek microsomes, acyl-CoA synthesis was stimulated by increasing concentrations of CoASH (Fig.2). In the absence of exogenously added CoASH, no acyl-CoA was detected (Fig.2). However, elongation of 18 carbon acyl chain was higher in the absence of CoASH than in the presence of CoASH, regardless of concentration (Fig.3). Elongation of 20 carbon acyl chain was stimulated with CoASH (Fig.3). 

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