Entry M0237    pteridine reductase

Previous Step     Next Step

Step 02

The dihydrobiopterin intermediate tautomerises.

GIF of Reaction Step M0237.stg02

Comment: Before this step occurs the dihydrobiopterin must dissociate from the active site, followed by NADP+. A second molecule of NADPH can then bind to the active site, followed by dihydrobiopterin. It is unclear whether the dihydrobiopterin is deprotonated (the base most likely to be the phosphate of the NADPH) or whether it retains the proton, with the intermediate stabilised by the negative charge of the NADPH phosphates. We have assumed that the proton remains associated with the dihydrobiopterin.


Proton Transfer
Assisted Keto-Enol Tautomerisation

Mechanism Components

Bond Cleavage
Bond Formation
Bond Order Change
Bond Polarisation
Intermediate Formation

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Arg14 Side Chain spectator Hydrogen Bond Donor
Electrostatic Stabiliser
Asp161 Side Chain spectator Hydrogen Bond Acceptor
Hydrogen Bond Donor
Tyr174 Side Chain spectator Hydrogen Bond Donor

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved
The C-N bond changes from a single to double bond
The C-O bond changes from a double to single bond

View similar reactions in MACiE.