Niacin Vitamin B3

1
Niacin (Vitamin B3)
O
C
Nicotinic acid ( niacin )
OH
N
O
C
Nicotinamide ( niacinamide )
NH2
N
2
Coenzyme Forms ??? Niacin
Oxidized forms

• Nicotinamide adenine dinucleotide
• ( NAD )
• Nicotinamide adenine dinucleotide
• phosphate ( NADP )

Reduced forms

• NADH
• NADPH

3
Reduced form
???? P
Nicotinamide adenine dinucleotide ( NAD )
Nicotinamide adenine dinucleotide phosphate (
NADP )
????? http//www.indstate.edu/thcme/mwking/vitam
ins.html
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?????????? NAD ??? NADP

• ????????????? coenzymes ??? enzymes
  oxidoreductases
• ???? dehydrogenases ???????????? lactate
  dehydrogenase,
• malate dehydrogenase.

alcohol dehydrogenase
CH3CH2OH NAD
CH3CHO NADH H
NAD 2e - 2 H
NADH H
5
AH2 NAD
A NADH H
oxidoreductase / dehydrogenase
AH2 NADP
A NADPH H
AH2 reduced substrate A oxidized substrate
H ( proton )
2 H
( 2e - 2H)
H - ( hydride ion )
6
NAD ??? NADP
NAD (oxidized)
????? Nelson and Cox, 2000
7
????? Nelson and Cox, 2000
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????? Murray et al, 1996
9
RIBOFLAVIN ( VITAMIN B2 )
D - ribitol ( sugar alcohol )
7,8 - dimethyl isoalloxazine ring
FAD
Riboflavin ????????????????? prosthetic group 2
???? ??? FMN (flavin mononucleotide ) ??? FAD (
flavin adenine dinucleotide )
????? http//www.indstate.edu/thcme/mwking/vitam
ins.html
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???????????? oxidized ??? reduced FMN ??? FAD
????? Nelson and Cox, 2000
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BIOSYNTHESIS ??? FMN ??? FAD
Riboflavin
ATP
flavokinase
ADP
FMN
ATP
FAD pyrophosphorylase
PPi
FAD
12
Flavin Nucleotides

• Oxidized forms
• FMN ( flavin mononucleotide )
• FAD ( flavin adenine dinucleotide )
• Reduced forms
• FMNH2
• FADH2

13
?????????? Flavin Nucleotides

• ????????????? prosthetic groups ??? enzymes ???
  
• oxidoreductases ???? dehydrogenases ????
• succinate dehydrogenase, dihydrolipoyl
  dehydrogenase

H
H
FAD ( FMN ) R-C-C-R
FADH2 ( FMNH2 ) R-CC-R
( yellow )
( colorless )
H
H
H
H
14
????? Nelson and Cox, 2000
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Lipoic Acid
CH2
CH2
CH
( CH2 )4
COOH
S
S
oxidized form
CH2
CH2
CH
( CH2 )4
COOH
SH
SH
reduced form
16
?????????? Lipoic Acid

• ????????????? prosthetic group ??? enzyme
  dihydrolipoyl
• transacetylase ( E2 ), enzyme ????????????
  pyruvate
• dehydrogenase complex ( multienzyme complex
  )
• ????????????? carrier ??? H ??? acyl group
  ????
• acetyl group

O
O
R - C -
Acyl group
CH3 - C -
Acetyl group
17
Lipoic Acid (Lipoate)??????????????????? Lysine
???? Amide Linkage
????? Nelson and Cox, 2000
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BIOTIN
Imidazole derivative
????? http//www.indstate.edu/thcme/mwking/vitam
ins.html
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N-Biotinyl-L-Lysine (Biocytin)
O
reactive group
C
HN
NH
carboxylase
HC
CH
O
O
CH
H2C
( CH2 )4
C - NH(CH2)4 - CH - C - ENZ
S
NH
e - amino group ??? R group side chain ???
lysine residue ??? carboxylase
amide bond
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?????????? Biotin

• ????????????? cofactor ???? prosthetic group
  ???
• enzymes ???????????????? carboxylation
  reactions
• ???? acetyl-CoA carboxylase ??? pyruvate
  carboxylase
• ????????????? carrier ??? carboxyl group
• ( -COOH )

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AVIDIN

• ???? glycoprotein , egg white protein
• ?? M.W. 70,000 D
• ???? heat labile
• ?????????? 4 polypeptide chains
• ??????????????????? biotin ????????????

biotin
biotin
Blood circulation
biotin
biotin