FAD – Flavin Adenine

Dinucleotide

FADIt derived from riboflavin, vitamin B2They have function in oxidation and reduction

reactionsFAD is act as coenzyme for various enzymes like α-ketoglutarate dehydrogenase, succinate dehydrogenase, xanthine dehydrogenase, acyl co dehydrogenase .

It exist in three different redox states, which are,1. Quinone (FAD) - fully oxidized form2. Semiquinone (FADH) -half reduced form3. Hydroquinone (FADH2) - fully reduced form

STRUCTURE OF FAD Flavin adenine dinucleotide consists of two main portions an adenine nucleotide (adenosine monophosphate) a flavin mononucleotide It is bridged together through their phosphate groups.

Riboflavin is formed by a carbon-nitrogen (C-N) bond between a isoalloxazine and a ribitol.

STRUCTURE OF FAD

FAD can be reduced to FADH2 through by the addition of two H+ and two e-.

Basic Physical and Chemical Properties

Based on the oxidation state, flavins take specific colors when in aqueous solution.

FAD (fully oxidized) is yellow, FADH(half reduced) is either blue or red

based on the pH, FADH2the fully reduced form is colorless

FAD Chemical States

Biosynthesis of FADFAD plays a major role as an enzyme

cofactor originating from riboflavin.Bacteria, fungi and plants can produce

riboflavin, but other eukaryotes, such as humans, have lost the ability to make it.

humans must obtain riboflavin, also known as vitamin B2, from dietary sources.

Riboflavin is generally absorbed in the small intestine and then transported to cells via carrier proteins.

FAD is synthesized in the cytosol and mitochondria and potentially transported where needed.

Step 1Riboflavin kinase (EC 2.7.1.26) adds a

phosphate group to riboflavin to produce flavin mononucleotide.

Step 2FAD synthetase attaches an adenine

nucleotide; both steps require ATP .

Biosynthesis

Biological Functions and Importance

catalyze difficult redox reactions such as dehydrogenation of a C-C bond to an alkene

FAD has a more positive reduction potential than NAD+ and is a very strong oxidizing agent.

FAD plays a major role as an enzyme cofactor FAD-dependent proteins function in a large

variety of metabolic pathways,electron transport, role in production of ATP The reduced coenzyme FADH2 contributes to oxidative phosphorylation in the mitochondria. FADH2 is reoxidized to FAD, which makes it possible to produce 1.5 equivalents of ATP.

DNA repair nucleotide biosynthesis FAD-dependent enzymes that regulate metabolism are glycerol-3-phosphate dehydrogenase (triglyceride synthesis) and xanthine oxidase involved in purine nucleotide catabolism beta-oxidation of fatty acids redox flavoproteins that non-covalently bind to FAD like Acetyl-CoA-dehydrogenases which are involved in beta-oxidation of fatty acidsamino acid catabolism catabolism of amino acids like leucine (isovaleryl-CoA dehydrogenase), isoleucine, (short/branched-chain acyl-CoA dehydrogenase), valine (isobutyryl-CoA dehydrogenase), and lysine synthesis of other cofactors such as CoA, CoQ and

heme groups.

EXAMPLES OF FAD DEPENDENT ENZYEMS

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