2. FAD
It derived from riboflavin, vitamin B2
They have function in oxidation and reduction reactions
FAD 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 form
2. Semiquinone (FADH) -half reduced form
3. Hydroquinone (FADH2) - fully reduced form
3. 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.
6. FAD can be reduced to FADH2 through by the
addition of two H+ and two e-.
7.
8. 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
10. Biosynthesis of FAD
FAD 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.
11. FAD is synthesized in the cytosol and
mitochondria and potentially transported where
needed.
Step 1
Riboflavin kinase (EC 2.7.1.26) adds a phosphate
group to riboflavin to produce flavin
mononucleotide.
Step 2
FAD synthetase attaches an adenine nucleotide;
both steps require ATP .
13. 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.
14. 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 acids
amino 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.