A microsomal enzyme system called fatty acyl-CoA desaturase is responsible for the formation of unsaturated fatty acids. This reaction also involves flavin-dependent cytochrome b5 reductase NADH and O2. The monounsaturated fatty acids, namely oleic and palmitoleic acids, are synthesised from stearic acid and palmitic acid, respectively. Mammals lack the ability to introduce double bond in…
The sequence of reactions for the synthesis of fatty acid (palmitate) is shown below. The carbon chain attached to ACP is transferred to cysteine residue, and reactions 1 to 4 are repeated 6 more times. Each time, the fatty acid chain is lengthened by a two-carbon unit. At the end of the seventh cycle, the…
Acetyl-CoA carboxylase has a requirement for the vitamin biotin. This is an ATP-dependent reaction biotin for carbon fixation. The mechanism of action of acetyl-CoA carboxylase is similar to that of pyruvate carboxylase. Acetyl-CoA carboxylase is the regulatory enzyme in fatty acid synthesis.
It converts malate to pyruvate. NADPH and CO2 are regenerated in this reaction. Both of them are utilised for fatty acid synthesis.
Acetyl-CoA and NADPH are pre-resquisites for fatty acid synthesis. Acetyl-CoA is produced in the mitochondria by the oxidation of pyruvate and fatty acids and degradation of carbon skeletons of amino acids and from ketone bodies. Mitochondrion is not permeable to acetyl-CoA, so Acetyl-CoA condenses with oxaloacetate in mitochondria to form citrate. Citrate lyase liberates Acetyl-CoA…
Fatty acid synthase is a dimmer composed of two identical subunits (monomers), each with a molecular weight of 240,000. Each subunit contains the activities of seven enzymes of FAS an ACP (acyl-carrier protein) with 4′-phosphopantothiene SH group. The two subunits lie in anti-parallel (head to tail) orientation. The SH group of phosphopantetheine of one subunit…
INTRODUCTION The dietary carbohydrates and amino acids, when consumed in excess, can be converted to fatty acids and stored as triglycerols. De novo (new) synthesis of fatty acids occurs predominantly in liver, kidney, adipose tissue, and lactating mammary glands. The enzyme machinery for the fatty acid production is located in cytosomal fraction of the cell.…
β-oxidation is the most predominant pathway for fatty acid degradation. However, the removal of one carbon unit at a time by oxidation of α-carbon atom of fatty acid is known as α-oxidation. This type of oxidation has been detected in brain tissues. It does not require CoA intermediates and does not require high energy phosphates.…
Due to the presence of double bonds, the unsaturated fatty acids are not reduced to some extent as saturated fatty acids. Therefore, oxidation of unsaturated fatty acids, in general, provides less energy than that of saturated fatty acids. This oxidation is overcome by two additional enzymes, isomerase and epimerase.