< Structural Biochemistry < Enzyme Catalytic Mechanism
General Information
Oxidation-reduction enzyme
Uses coenzymes NADP+/NADPH and FAD/FADH2
In humans, this is a dimer of 478-amino acid subunits linked by disulfide bond
Two-stage reaction
1st stage: E + NADPH + H+ EH2 + NADP+
Oxidized E binds NADPH, immediately reduces FAD, producing NADP+.
E contains redox-active disulfide bond (Cys58-Cys63), which has accepted an electron pair in EH2 to form a dithiol (one S- is in a charge transfer complex with FADH-)
2nd stage: EH2 + GSSG E + 2GSH
GSSG binds to EH2
Cys58 nucleophile attacks one S of GSSG yielding mixed disulfide, promoted by His467' acting as general base
One GSH is kicked-off by protonation by His467' (general acid)
Cys63 nucleophile attacks Cys58 to form redox-active disulfide, kicking off second GSH
Reference
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