Which of the following is multi-enzyme complex?
Ans. c (Fatty acid synthase). (Ref. Harper's biochemistry 27th ed. Pg. 238 Chapter 23)KEY STEPS OF FATTY ACID SYNTHESIS# Fatty acid entry into mitochondrion is via Camiitine shuttle.2# Fatty acid entry into cytosol is via Carnitine shuttle.# Fatty acid synthase is a polypeptide multi-enzyme complex.2# Acyl carrier protein is a integral part of this polypeptide complex and functions as CoA.# Being a single unit; great efficiency freedom from interference and co-ordinated synthesis of all enzymes encoded by a single gene as advantage of this fatty acid synthase multi-enzyme complex.# Another example of multienzyme complex is:- pyruvate dehydrogenase complex (complex contains 3 enzymes that require 5 cofactors).The Fatty Acid Synthase Complex Is a Polypeptide Containing Seven Enzyme Activities# In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP).# However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4'-phosphopantetheine.# In mammals, the fatty acid synthase complex is a dimer comprising two identical monomers, each containing all seven enzyme activities of fatty acid synthase on one polypeptide chain. Initially, a priming molecule of acetyl-CoA combines with a cysteine --SH group catalyzed by acetyl transacylase.# Malonyl-CoA combines with the adjacent --SH on the 4'-phosphopantetheine of ACP of the other monomer, catalyzed by malonyl transacylase (reaction lb), to form acetyl (acyl)-malonyl enzyme.# It is liberated from the enzyme complex by the activity of a seventh enzyme in the complex, thioesterase (deacylase).# The free palmitate must be activated to acyl-CoA before it can proceed via any other metabolic pathway. Its usual fate is esterification into acylglycerols, chain elongation or desaturation, or esterification to cholesteryl ester.# In mammary gland, there is a separate thioesterase specific for acyl residues of C8, C10, or C12, which are subsequently found in milk lipids.
HMG-CoA synthase
Malic enzyme
Fatty acid synthase
Fatty acid oxidase
Enzymes