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Biosynthesis of Fatty Acids and Eicosanoids: -The Fatty Acid Synthase Complex Has Seven Different Active Sites

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  789-790

2026-06-29

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Biosynthesis of Fatty Acids and Eicosanoids: -The Fatty Acid Synthase Complex Has Seven Different Active Sites

The core of the E. coli fatty acid synthase system con sists of seven separate polypeptides (Table 21–1), and at least three others act at some stage of the process. The proteins act together to catalyze the formation of fatty acids from acetyl-CoA and malonyl-CoA. Throughout the process, the intermediates remain covalently at tached as thioesters to one of two thiol groups of the synthase complex. One point of attachment is the OSH group of a Cys residue in one of the seven synthase proteins (β-ketoacyl-ACP synthase); the other is the OSH group of acyl carrier protein.

Acyl carrier protein (ACP) of E. coli is a small protein (Mr 8,860) containing the prosthetic group 4-phosphopantetheine (Fig. 21–4; compare this with the panthothenic acid and β-mercaptoethylamine moiety of coenzyme A in Fig. 8–41). Hydrolysis of thioesters is highly exergonic, and the energy released helps to make two different steps (1 and 5 in Fig. 21–5) in fatty acid synthesis (condensation) thermodynamically favorable. The 4-phosphopante-theine prosthetic group of ACP is believed to serve as a flexible arm, tethering the growing fatty acyl chain to the surface of the fatty acid synthase complex while carrying the reaction intermediates from one enzyme active site to the next.

FIGURE 21–4 Acyl carrier protein (ACP). The prosthetic group is 4 phosphopantetheine, which is covalently attached to the hydroxyl group of a Ser residue in ACP. Phosphopantetheine contains the B vitamin pantothenic acid, also found in the coenzyme A molecule. Its OSH group is the site of entry of malonyl groups during fatty acid synthesis.