Basic Pathways of Fatty Acid and Acyl Lipid Metabolism

BASIC PATHWAYS OF FATTY ACID AND ACYL LIPID METABOLISM 

De novo formation of fatty acids in plants requires the concerted action of acetyl-CoA carboxylase and fatty acid synthetase. In most plants, these 

Purification procedures for acetyl-CoA carboxylase usually use an affinity step with avidin attached to the column matrix. This allows a more rapid purification to take place and is important since, even with proteinase 

Acetyl-CoA ACP transacylase is a thiolactomycin-sensitive enzyme which catalyzes what has often been regarded as the slowest of all the partial reactions. However, the recent observation that in spinach leaves and all other plant tissues examined there is an acetoacetyl-ACP synthetase which bypasses this reaction (and which has much higher activity) sheds doubt on the physiological importance of acetyl-CoA ACP transacylase. The acetoacetyl-ACP synthetase, sometimes called the short-chain condensing enzyme, is cerulenin insensitive and can, therefore, be differentiated easily from the )8-ketoacyl-ACP synthetase I, which is the main condensing enzyme. The latter has been purified recently to homogeneity for the first time.  

It is well known that the two-carbon units for condensation in de novo fatty acid synthesis are provided as malonate. A specific transacylase transfers the malonate from coenzyme A to ACP. Malonyl-CoA ACP transacyl-ases have been purified from a number of sources including leaf and seed tissues as well as the cyanobacterium Anabaena variabilis. The enzymes usually have masses of about 40 kDa and appear to use a random sequence mechanism. Tissue-specific isoforms have been reported in some instances though their significance is not known. 

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