Substrate specificity of formylglycinamidine synthetase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Formylglycinamidine ribonucleotide (FGAM) synthetase catalyzes a key step in purine biosynthesis.
• Previous purification methods exist, but alternative approaches can yield higher specific activity.

Purpose of the Study:

• To purify FGAM synthetase from chicken liver using an alternative procedure.
• To investigate the substrate specificity of FGAM synthetase using novel analogues of formylglycinamide ribonucleotide (FGAR).

Main Methods:

• Purification of FGAM synthetase to homogeneity.
• Synthesis and characterization of FGAR analogues using 1H and 13C NMR spectroscopy.
• Enzyme assays measuring inorganic phosphate (Pi) production and glutaminase activity.
• Analysis of enzyme-substrate complexes using Sephadex G-50 chromatography.
• Isotopic labeling ([18O]-beta-FGAR) and 31P NMR spectroscopy to trace oxygen transfer.

Main Results:

• A new purification protocol yielded FGAM synthetase with higher specific activity (0.20 mumol min-1 mg-1) compared to previous methods.
• Several FGAR analogues were synthesized and characterized.
• FGAM synthetase demonstrated varying degrees of ATPase activity with different analogues, with R = CH2NHCOCH3 showing significant activity and conversion to the amidine analogue.
• The enzyme showed high specificity for the formylglycine side chain of FGAR.
• 31P NMR confirmed the transfer of amide oxygen from FGAR to inorganic phosphate during catalysis.

Conclusions:

• The alternative purification method is effective for obtaining highly active FGAM synthetase.
• FGAM synthetase exhibits strict specificity for the formylglycine moiety of its substrate.
• The catalytic mechanism involves the transfer of the amide oxygen to inorganic phosphate.