Final answer:
FAS stands for Fatty Acid Synthase, which is an enzymatic complex responsible for the biosynthesis of fatty acids in eukaryotic organisms. This complex consists of two identical multifunctional polypeptides and utilizes NADPH as a reducing agent during the synthesis process.
Step-by-step explanation:
Definition and Role of Fatty Acid Synthase (FAS)
FAS stands for Fatty Acid Synthase, which is a complex enzyme responsible for biosynthesis of fatty acids. In eukaryotes, FAS operates on a large, multifunctional enzymatic complex. This complex consists of two identical multifunctional polypeptides with three catalytic domains located on the N-terminal side, which include ketoacyl synthase (KS), malonyl /acetyl-transferase (MAT), and dehydrase (DH). These domains are followed by a core region, leading to the C-terminal side with four other domains: enoyl reductase (ER), ketoacyl reductase (KR), acyl carrier protein (ACP), and thioesterase (TE).
The ACP domain contains a phosphopantetheine group with an active sulfhydryl group that is essential for the attachment and growth of the fatty acid chain. Another sulfhydryl group is provided by a cysteine residue of 3-ketoacyl-ACP synthase enzyme. The entire complex functions as a dimer, with biosynthesis of fatty acids proceeding through a series of reactions, finally yielding palmitate after seven cycles. During this process, NADPH is utilized as a reducing agent, often provided by the HMP pathway.
The understanding of FAS and fatty acid biosynthesis is crucial for studying various metabolic processes such as the metabolism of fatty acids, cholesterol biosynthesis, bile acid metabolism, lipoprotein metabolism, and conditions like fatty liver.