Pyridine nucleotide interaction with rat liver dihydropteridine reductase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Dihydropteridine reductase (DHPR) is a crucial enzyme in folate metabolism.
• Understanding DHPR's substrate interactions is key to its biological function.

Purpose of the Study:

• To investigate the binding interactions of purified rat liver DHPR with various nucleotides.
• To characterize the stability and properties of DHPR-nucleotide complexes.

Main Methods:

• Fluorescence titration
• Circular dichroism
• Equilibrium dialysis
• Sephadex G-25 chromatography
• Polyacrylamide gel electrophoresis

Main Results:

• DHPR exhibits a preference for NADH, binding one mole of NADH per mole of enzyme.
• The binary complex of DHPR with NADH is only partially stable, showing increased mobility in gel electrophoresis.
• The DHPR-NADH complex can be isolated via Sephadex G-25 chromatography and exhibits distinct spectral characteristics.
• No ternary complexes were observed with the pteridine product or methotrexate.

Conclusions:

• Rat liver DHPR forms a specific, albeit partially unstable, binary complex with NADH.
• The enzyme's interaction with NADH influences its electrophoretic mobility and spectral properties.
• DHPR does not appear to form stable ternary complexes with its pteridine substrate or methotrexate under these conditions.