Oxidoreductases catalyze redox reactions:

1

• Oxidoreductases catalyze redox reactions
• Aox Bred lt---gt Ared Box
• Subclasses Which group is the electron donor?
• 1.1. acting on OH groups
• 1.6. acting on NADPH, NADH
• 1.16. oxidizing metal ions

2

• One of the entries modified in 2005
  CoA-disulfide reductase
• Reaction
• 2 CoA NAD(P) ? CoA-disulfide NAD(P)H H
  
• Originally, this enzyme was entered as EC
  1.6.4.10 (acting on NADH), 2002 it was
  transferred to 1.8.1.14 (acting on a sulfur group
  of donors ). 2005 distinction depending on
  cofactor specificty (NADPH or NAD(P)H)

3

• Proteinogenic amino acids
• Only Cys and Sec (selenocysteine) are
  redoxactive.
• Cys is mostly used to keep other sufhydryl groups
  in their proper redox state disulfide
  isomerases.

4

• Glutathione peroxidase
• Overall reaction
• ROOH 2 GSH --gt ROH GSSG H2O

5

• Glutathione peroxidase

Sec is a good nucleophile and reversibly
oxidizable.
6

• Metal cofactors
• Transition row metal ions are often involved in
  redox reactions Mn, Fe, Co, Ni, Cu
• There are mononuclear sites, clusters with and
  without small ligands (S2-, O2-), and cations as
  part of larger cofactors (tetrapyrrols, MoCo).

7

• Superoxide dismutase
• Overall reaction
• 2 OO- 2 H --gt O2 H2O2

8

• Superoxide dismutase

Cu2, square planar, pale blue
Cu1, trigonal pyramidal, colorless
9

• Superoxide dismutase

10

• Coordination types of Cu2 Redox potentials
• Type I (blue copper), trigonal bipyramidal 300
  (200-700) mV
• (eq His, His, Cys ax Met, carbonyl)
• Type II, square planar, two distant axial
  ligands 150 mV (H2O), 390 mV (laccase)
• (eq His, Glu, His, Glu)
• Type III, Cu-Cu pair
• (six His)
• Superoxide dismutase
• Tetrahedral
• (His, His, His, solvent)

11
oxidized square planar
reduced tetrahedral
12

• Other cofactors
• One electron transfers FAD, (NAD)
• Two electron transfers NAD, Liponamid, FAD, FMN

13

• D-Amino acid oxidase (FAD)
• Overall reaction
• Tasks Proton abstraction (or hydride?) at C-1
  and oxidation at C-1

14
1

• D-Amino acid oxidase (FAD)
• The proton from the substrate ends up on N-1 of
  FAD, but only after reduction of the flavin,
  because the oxidized flavin is no base.
• The electrons are transferred via a covalent
  intermediate to C-4a.
• FlavinH2 oxidized pKa ltlt 0
• FlavinH2 reduced pKa 6.3

4a
15

• Alcohol dehydrogenase
• Overall reaction
• R1R2CHOH NAD --gt R1R2CO NADH/H

16

• Alcohol dehydrogenase
• The Zn2 increases the acidity of the alcohol,
  but is not involved in the redox reaction.

17

• Alcohol dehydrogenase
• Path of the abstracted proton.
• The His is in contact to the bulk solvent.
• Burst kinetics show a pKa of 6.4 -gt His?

18

• Alcohol dehydrogenase
• Only one of the enantiotopic protons of EtOH is
  abstracted and is added to a specific side of
  NAD.