Malonyl coenzyme A

A second molecule of acetyl coenzyme A reacts with carbon dioxide (actually bicarbonate ion at biological pH) to give malonyl coenzyme A... 

Formation of malonyl coenzyme A is followed by a nucleophilic acyl substitution which transfers the malonyl group to the acyl carrier protein as a thioester... 

The four carbon atoms of the butanoyl group originate m two molecules of acetyl coenzyme A Carbon dioxide assists the reaction but is not incorporated into the prod uct The same carbon dioxide that is used to convert one molecule of acetyl coenzyme A to malonyl coenzyme A is regenerated m the decarboxylation step that accompanies carbon-carbon bond formation... 

The introduction to Section 26 8 pointed out that mevalonic acid is the biosynthetic pre cursor of isopentenyl pyrophosphate The early steps m the biosynthesis of mevalonate from three molecules of acetic acid are analogous to those m fatty acid biosynthesis (Sec tion 26 3) except that they do not involve acyl earner protein Thus the reaction of acetyl coenzyme A with malonyl coenzyme A yields a molecule of acetoacetyl coenzyme A... 

Section 26 3 The biosynthesis of fatty acids follows the pathway outlined in Figure 26 3 Malonyl coenzyme A is a key intermediate... 

Fatty acids derived from animal and vegetable sources generally contain an even number of carbon atoms siace they are biochemically derived by condensation of two carbon units through acetyl or malonyl coenzyme A. However, odd-numbered and branched fatty acid chains are observed ia small concentrations ia natural triglycerides, particularly mminant animal fats through propionyl and methylmalonyl coenzyme respectively. The glycerol backbone is derived by biospeciftc reduction of dihydroxyacetone. 

JEZ, J.M., FERRER, J.-L., BOWMAN, M.E., DIXON, R.A., NOEL, J.P., Dissection of malonyl-coenzyme A decarboxylation from polyketide formation in the reaction mechanism of a plant polyketide synthase, Biochemistry, 2000, 39, 890-902. 

Serine hydroxymethyl transferase catalyzes the decarboxylation reaction of a-amino-a-methylmalonic acid to give (J )-a-aminopropionic acid with retention of configuration [1]. The reaction of methylmalonyl-CoA catalyzed by malonyl-coenzyme A decarboxylase also proceeds with perfect retention of configuration, but the notation of the absolute configuration is reversed in accordance with the CIP-priority rule [2]. Of course, water is a good proton source and, if it comes in contact with these reactants, the product of decarboxylation should be a one-to-one mixture of the two enantiomers. Thus, the stereoselectivity of the reaction indicates that the reaction environment is highly hydro-phobic, so that no free water molecule attacks the intermediate. Even if some water molecules are present in the active site of the enzyme, they are entirely under the control of the enzyme. If this type of reaction can be realized using synthetic substrates, a new method will be developed for the preparation of optically active carboxylic acids that have a chiral center at the a-position. 

Kreuzaler F, Hahlbrock K (1972) Enzymatic synthesis of aromatic compounds in higher plants formation of naringenin (5,7,4 -trihydroxyflavanone) from p-coumaroyl coenzyme A and malonyl coenzyme A. FEBS Lett 28(l) 69-72... 

Suzuki, H. et al., cDNA cloning, heterologous expressions, and functional characterization of malonyl-coenzyme A anthocyanidin 3-0-glucoside-6"-0-malonyltransferase from dahlia flowers. Plant Physiol, 130, 2142, 2002. 

Yamaguchi, M. et al., Cyanidin 3-malonylglucoside and malonyl-coenzyme A anthocyanidin malonyltransferase in Lactuca sativa leaves. Phytochemistry, 42, 661, 1996. 

The biosynthesis of the polyketide moiety is thought to involve the condensation of coenzyme A esters of acetic acid with malonyl coenzyme A to give thiol esters of 3-keto acids. Further Claisen condensations with malonyl coenzyme A add further ketone units, leading to 3,5-diketo, 3,5,7-triketo acids and so on as their thiol esters. Intramolecular condensations subsequently afford heterocyclic or aromatic structures (Scheme 275). 

Section 26.4 HOCCH2CSCoA Malonyl coenzyme A Phospholipids are intermediates in the biosynthesis of triacylglycerols from fatty acids and are the principal constituents of the lipid bilayer component of cell membranes. O rcoch2 o O CHOCR (HO)2POCH2 A phospholipid... 

B Shell, CR Hutchinson. Enzymatic synthesis of a bacterial polyketide from acetyl and malonyl coenzyme A. Science 262 1535-1540, 1993. 

Thus, hypotheses a and c, which demanded participation of a Cg-Cj unit in the biosynthesis of the phenylquinolizidine moiety, have been disproved. The mode of incorporation of lysine and its metabolites has eliminated routes b and d. The accumulative evidence demonstrates that only path e is consistent with all experimental results. This route predicts an extension of the side chain of the phenylpropanoid precursor by a two-carbon unit supplied by a donor such as acetyl- or malonyl-Coenzyme A. The results of the final experiment with [2-14C]malonate were consistent with hypothesis e but inconclusive. 

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