26.3 Fatty Acid Biosynthesis 1021 Step 1: An acetyl group is transferred to the a carbon atom of the malonyl group with evolution of carbon dioxide. Presumably decarboxylation gives an enol, which attacks the acetyl group ACP -O-C=0 CH C-CH, CS- ACP +-S-ACP C-CH CS-ACP Acetyl and malonyl groups bound to acyl acyl carrier Step 2: The ketone carbonyl of the acetoacetyl group is reduced to an alcohol function. This reduction requires NADPH as a coenzyme (NADPH is the phosphate ester of NADh and reacts similarly to it. CH CCH CS-ACP NADPh+ HO+ CH,CHCH,CS-ACP NADP+ H,O Reduced Hydronium Oxidized form of acyl carrier protein form of coenzyme Step 3: Dehydration of the B-hydroxy acyl group CH CHCH CS-ACP CHCH=CHCS一ACP+H2O S-ci carey brtateiy acyl carrier protein Step 4: Reduction of the double bond of the a, B-unsaturated acyl group. This step requires NADPH as a coenzyme CH ACP NADPH HO+ > CH CH-CH CS -ACP+ NADP++ Ho S-2-Butenoyl Reduced Hydronium S-Butanoyl Oxidized coenzym 26.3 Mechanism of PROBLEM 26.3 By analogy to the intermediates given in steps 1-4 of Figure hesis of a butanoyl 26.3, write the sequence of acyl groups that are attached to the acyl carrier pro- rom acetyl and mal tein in the conversion of onyl building blocks CH3(CH2)12CS-ACP to CH3(CH2)14CS-ACP Back Forward Main MenuToc Study Guide ToC Student o MHHE Website26.3 Fatty Acid Biosynthesis 1021 PROBLEM 26.3 By analogy to the intermediates given in steps 1–4 of Figure 26.3, write the sequence of acyl groups that are attached to the acyl carrier pro￾tein in the conversion of CH3(CH2)12CS±ACP to O X CH3(CH2)14CS±ACP O X Step 1: An acetyl group is transferred to the carbon atom of the malonyl group with evolution of carbon dioxide. Presumably decarboxylation gives an enol, which attacks the acetyl group. Step 2: The ketone carbonyl of the acetoacetyl group is reduced to an alcohol function. This reduction requires NADPH as a coenzyme. (NADPH is the phosphate ester of NADH and reacts similarly to it.) CH3C O S ACP O O C CH2CS O ACP Acetyl and malonyl groups bound to acyl carrier protein O C O CH3C O CH2CS O ACP S ACP Carbon dioxide S-Acetoacetyl acyl carrier protein Acyl carrier protein (anionic form) CH3CCH O 2CS O ACP S-Acetoacetyl acyl carrier protein NADPH Reduced form of coenzyme H3O Hydronium ion CH3CHCH2CS O ACP S-3-Hydroxybutanoyl acyl carrier protein NADP Oxidized form of coenzyme H2O Water OH Step 3: Dehydration of the -hydroxy acyl group. CH3CHCH2CS O ACP S-3-Hydroxybutanoyl acyl carrier protein OH CH3CH CHCS O ACP S-2-Butenoyl acyl carrier protein H2O Water Step 4: Reduction of the double bond of the , -unsaturated acyl group. This step requires NADPH as a coenzyme. CH3CH CHCS O ACP S-2-Butenoyl acyl carrier protein NADPH Reduced form of coenzyme H3O Hydronium ion CH3CH CH2CS O ACP S-Butanoyl acyl carrier protein NADP Oxidized form of coenzyme H2O Water 2 FIGURE 26.3 Mechanism of biosynthesis of a butanoyl group from acetyl and mal￾onyl building blocks. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website