Elongation-decarboxylation mechanism

The effects of environmental factors such as light and temperature on the synthesis of alkanes and very long acids support the elongation-decarboxylation mechanism. For example, the synthesis of /1-C29 alkane and its oxygenated derivatives was increased by intense light, while the formation... 

The final and perhaps the most convincing evidence for the elongation-decarboxylation mechanism was provided by the demonstration that cell-free extracts fromi. sativum leaves catalyzed conversion of [9,10,11- H]C32 acid to C31 alkane (Khan and Kolattukudy, 1974). In such preparations both C31 and C30 alkanes were generated from the labeled C32 acid, suggesting that such preparations catalyzed a-oxidation in addition to decarboxylation of fatty acids to alkanes. Imidazole, an inhibitor of a-oxidation (Shine and Stumpf, 1974), inhibited the formation of both /1-C30 and -C3i alkanes from C32 acid, suggesting that an a-oxidation-type reaction was involved in the conversion of C32 acid to C31 alkane (Table VI). In support of this hypothesis... 

Chan Yong, T.P., C. Largeau, and E. Casadevall Biosynthesis of non-isoprenoid hydrocarbons by the microalga Botryococcus braunii. Evidence for an elongation-decarboxylation mechanism. Activation of decarboxylation. Nouv. J. de Chimie 10, 701 (1986). 

Fig. 3 Proposed biosynthetic pathways for the production of the sex pheromone components in the indicated insects. Common mechanisms include fatty acid synthesis, desaturation, chain elongation, and decarboxylation...

Methylthiobutyl glucosinolate derives from L-methionine by a complex elongation process leading to dihomomethionine. Four of the five carbons of methionine are retained, one being lost in a decarboxylation. The two necessary additional carbons each derive from a methyl group of acetyl-S-CoA by a complex, multi-step condensation mechanism (Equation 11) ... 

In the synthesis of fatty acids the acetyl irnits are condensed and then are reduced to form straight hydrocarbon chains. In the oxo-acid chain elongation mechanism, the acetyl unit is introduced but is later decarboxylated. Tlius, the chain is increased in length by one carbon atom at a time. These two mechanisms account for a great deal of the biosynthesis by chain extension. However, there are other variations. For example, glycine (a carboxylated methylamine), under the influence of pyridoxal phosphate and with accompanying decarboxylation, condenses with succinyl-CoA (Eq. 14-32) to extend the carbon chain and at the same time to introduce an amino group. Likewise, serine (a carboxylated ethanolamine) condenses with... 

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]. 

BaeL KSS and PsyA KS2 are located immediately before and after -branching enzymes, which install a -methyl and a fi-methylene branch respectively (Scheme 3.2). In each instance, the mechanism of ( -branch formation is essentially the same. The synthesis commences with decarboxylation of malonyl-ACP by a non-elongating KS, to yield acetyl-ACP. A 3-hydroxy-3-methylglutaryl-CoA... 

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