Amino acids straight-chain” pathway

Similar straight- and branched-chain fatty acids have been reported from other helminths, such as Echinostoma leie and Paragonimus westermani, and will surely be detected in other lumen-dwelling helminths with improved assay techniques. However, volatile acids, such a 2-methylbutanoate, can also be formed from the degradation of amino acids, so that their presence alone does not prove that the ascarid pathway is operative. This appears to be the case in F. hepatica. 

Branched Chain Adds. Three of the amino acids found as usual components of proteins, valine, leucine, and isoleucine, contain branched chains. The amino groups are lost in the first step of degradation (see Chapter VII), and the resulting a-keto acids are metabolized by specific pathways related to the pathways of straight-chain fatty acid metabolism. 

The discovery of a novel pathway for biosynthesis of medium and short chain fatty acids in plants (a-keto acid elongation pathway, 1) raises the possibility (however unlikely) that medium-chain fatty acids (mcFAs) of certain oil seeds producing them may be derived by this pathway. Alternatively, these may be formed after release of elongating fatty acid chains from fatty acid synthase mediated biosynthesis (FAS) by specific medium chain thioesterases [2, 3,4]. Thus far the aKAE pathway is only known to occur in trichome glands of plants in the family Solanaceae. In the aKAE pathway, iso-, anteiso- or straight-chain keto acid products of branched-chain amino acid metabolism are elongated by one carbon (via acetate) per cycle. The final step is predicted to be oxidative decarboxylation to yield CoA activated acids. The mechanism that determines the chain length of aKAE products is not understood [1]. 

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