An ultrafiltration assay for nucleotide binding to ribonucleotide reductase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Ribonucleotide reductase (RNR) is crucial for DNA synthesis and repair.
• Understanding nucleotide binding to RNR is essential for characterizing enzyme activity.
• Existing methods for studying nucleotide binding can be time-consuming or complex.

Purpose of the Study:

• To develop a rapid and reliable method for quantifying nucleotide binding to Escherichia coli ribonucleotide reductase.
• To validate the new method using known nucleotide substrates.
• To extend the understanding of ATP and dGTP binding kinetics.

Main Methods:

• Direct partition using ultrafiltration coupled with centrifugation.
• Separation of bound and unbound nucleotides over an ultrafiltration membrane.
• Measurement of dissociation constants for various nucleotides (dATP, ATP, dTTP, dGTP, GDP) at different temperatures (25°C and 4°C).

Main Results:

• The ultrafiltration assay effectively separated bound and unbound nucleotides within 0.5-1 minute.
• No adverse effects were observed due to protein hyperconcentration at the membrane surface.
• Dissociation constants determined by this method showed good agreement with previously reported data.
• The study provided new insights into ATP and dGTP binding at 25°C.

Conclusions:

• Ultrafiltration offers a fast and effective approach for studying nucleotide-RNR interactions.
• This method provides accurate binding data and can be applied to various nucleotide substrates.
• The findings contribute to a deeper understanding of ribonucleotide reductase function and regulation.