Flavin adenine dinucleotide and Related Topics

Human GSR with bound glutathione and FADH

Glutathione reductase

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Enzyme that in humans is encoded by the GSR gene.

General reaction catalyzed by glutathione reductase

Reduced glutathione reductase, glutathione peroxidase and glutathione interact to reduce hydrogen peroxide to water, in order to protect the cell from oxidative damage.

Graphical representation of overall reaction catalyzed by GR

Glutathione reductase functions as dimeric disulfide oxidoreductase and utilizes an FAD prosthetic group and NADPH to reduce one molar equivalent of GSSG to two molar equivalents of GSH:

Ribbon diagram of a monomer of human MAO-A, with FAD and clorgiline bound, oriented as if attached to the outer membrane of a mitochondrion. From.

Monoamine oxidase

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Monoamine oxidases (MAO) are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group.

Norepinephrine degradation. Monoamine oxidase is shown left in the blue box.

Monoamine oxidases contain the covalently bound cofactor FAD and are, thus, classified as flavoproteins.

A diagrammatic illustration of the process of lipolysis (in a fat cell) induced by high epinephrine and low insulin levels in the blood. Epinephrine binds to a beta-adrenergic receptor in the cell membrane of the adipocyte, which causes cAMP to be generated inside the cell. The cAMP activates a protein kinase, which phosphorylates and thus, in turn, activates a hormone-sensitive lipase in the fat cell. This lipase cleaves free fatty acids from their attachment to glycerol in the fat stored in the fat droplet of the adipocyte. The free fatty acids and glycerol are then released into the blood. However more recent studies have shown that adipose triglyceride lipase has to first convert triacylglycerides to diacylglycerides, and that hormone-sensitive lipase converts the diacylglycerides to monoglycerides and free fatty acids. Monoglycerides are hydrolyzed by monoglyceride lipase. The activity of hormone sensitive lipase is regulated by the circulation hormones insulin, glucagon, norepinephrine, and epinephrine, as shown in the diagram.

Fatty acid metabolism

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Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category.

A diagrammatic illustration of the transport of free fatty acids in the blood attached to plasma albumin, its diffusion across the cell membrane using a protein transporter, and its activation, using ATP, to form acyl-CoA in the cytosol. The illustration is, for diagrammatic purposes, of a 12 carbon fatty acid. Most fatty acids in human plasma are 16 or 18 carbon atoms long.

A diagrammatic illustration of the transfer of an acyl-CoA molecule across the inner membrane of the mitochondrion by carnitine-acyl-CoA transferase (CAT). The illustrated acyl chain is, for diagrammatic purposes, only 12 carbon atoms long. Most fatty acids in human plasma are 16 or 18 carbon atoms long. CAT is inhibited by high concentrations of malonyl-CoA (the first committed step in fatty acid synthesis) in the cytoplasm. This means that fatty acid synthesis and fatty acid catabolism cannot occur simultaneously in any given cell.

A diagrammatic illustration of the process of the beta-oxidation of an acyl-CoA molecule in the mitochodrial matrix. During this process an acyl-CoA molecule which is 2 carbons shorter than it was at the beginning of the process is formed. Acetyl-CoA, water and 5 ATP molecules are the other products of each beta-oxidative event, until the entire acyl-CoA molecule has been reduced to a set of acetyl-CoA molecules.

Example of an unsaturated fat triglyceride. Left part: glycerol, right part from top to bottom: palmitic acid, oleic acid, alpha-linolenic acid. Chemical formula: C55H98O6

Chemical structure of the diglyceride 1-palmitoyl-2-oleoyl-glycerol

Dietary fats are emulsified in the duodenum by soaps in the form of bile salts and phospholipids, such as phosphatidylcholine. The fat droplets thus formed can be attacked by pancreatic lipase.

Structure of a bile acid (cholic acid), represented in the standard form, a semi-realistic 3D form, and a diagrammatic 3D form

Diagrammatic illustration of mixed micelles formed in the duodenum in the presence of bile acids (e.g. cholic acid) and the digestion products of fats, the fat soluble vitamins and cholesterol.

Synthesis of saturated fatty acids via Fatty Acid Synthase II in E. coli

1) Dehydrogenation by acyl-CoA dehydrogenase, yielding 1 FADH2

Adrenodoxin reductase

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First isolated from bovine adrenal cortex where it functions as the first enzyme in the mitochondrial P450 systems that catalyze essential steps in steroid hormone biosynthesis.

Adrenodoxin reductase is a flavoprotein as it carries a FAD type coenzyme.

Adrenal ferredoxin

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Protein that in humans is encoded by the FDX1 gene.

The first enzyme in this system is adrenodoxin reductase that carries an FAD.

Glutaryl-CoA dehydrogenase

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Enzyme encoded by the GCDH gene on chromosome 19.

The flavin adenine dinucleotide (FAD) is located at the junction between the middle beta-strand and the carboxyl terminal alpha-helix domain of one subunit and the carboxyl-terminal domain of the neighboring subunit.

crystal structure of the n-(1-d-carboxylethyl)-l-norvaline dehydrogenase from arthrobacter sp. strain 1c

Glycerol-3-phosphate dehydrogenase

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Enzyme that catalyzes the reversible redox conversion of dihydroxyacetone phosphate (a.k.a. glycerone phosphate, outdated) to sn-glycerol 3-phosphate.

Fig. 1. Schematic overview of fermentative and oxidative glucose metabolism of Saccharomyces cerevisiae. (A) upper part of glycolysis, which includes two sugar phosphorylation reactions. (B) fructose-1,6-bisphosphate aldolase, splitting the C6-molecule into two triose phosphates (C) triosephosphate isomerase, interconverting DHAP and GAP. (D) glycerol pathway reducing DHAP to glycerol-3-phosphate (G3P) by G3P dehydrogenase, followed by dephosphorylation to glycerol by G3Pase. (E) The lower part of glycolysis converts GAP to pyruvate while generating 1 NADH and 2 ATP via a series of 5 enzymes. (F) Alcoholic fermentation; decarboxylation of pyruvate by pyruvate decarboxylase, followed by reduction of acetaldehyde to ethanol. (G) mitochondrial pyruvate-dehydrogenase converts pyruvate to acetyl-CoA, which enters the tricarboxylic acid cycle. (H) external mitochondrial NADH dehydrogenases. (I) mitochondrial G3P dehydrogenase. Electrons of these three dehydrogenases enter the respiratory chain at the level of the quinol pool (Q). (J) internal mitochondrial NADH dehydrogenase. (K) ATP synthase. (L) generalized scheme of NADH shuttle. (M) formate oxidation by formate dehydrogenase.

structure of glycerol-3-phosphate dehydrogenase from archaeoglobus fulgidus

Mitochondrial glycerol-3-phosphate dehydrogenase (GPD2), catalyzes the irreversible oxidation of glycerol-3-phosphate to dihydroxyacetone phosphate and concomitantly transfers two electrons from FAD to the electron transport chain.