A 263 GHz Pulse EPR System for Studying Metal-Binding Proteins

Overview

Researchers developed a 263 GHz pulse EPR system using a 10 W traveling-wave tube amplifier to study transition-metal ions in chemical and biological samples. In manganese-containing samples, it produced a 12.5-fold higher signal-to-noise ratio than a commercial X-band system under comparable conditions and distinguished manganese environments in two metal-binding proteins.

Background

Electron paramagnetic resonance (EPR) detects substances with unpaired electrons, including some metal ions, and can provide information about their chemical environment and interactions with nearby molecules. Transition metals participate in biological processes that include enzyme activity and immune defense. At lower EPR frequencies, signals from high-spin metal ions can broaden, obscuring features; very high-frequency pulse EPR has been constrained by limited access to powerful amplifiers. The reported system uses a high-power, broadband amplifier and operates without a resonant cavity.

Data Highlights

Key Findings

• The 263 GHz instrument delivered high-power pulses across a 5.6 GHz bandwidth using a 10 W traveling-wave tube amplifier.
• The system operated without a resonant cavity, enabling examination of larger samples, different sample shapes, and a wider range of frequencies.
• For trace manganese(II) in magnesium oxide, the reported signal-to-noise ratio was approximately 1,540, compared with 123 for a commercial X-band system under comparable conditions.
• The amplifier increased the signal by approximately ninefold, while the overall signal-to-noise ratio improvement over the X-band system was 12.5-fold.
• Measurements of manganese in frozen water, bound to EDTA, and incorporated into calprotectin and PsaA showed spectral differences reflecting the metal’s coordination, symmetry, and chemical environment.
• Calprotectin is involved in immune response and can withhold essential metals from microorganisms; PsaA helps certain bacteria acquire manganese.

Clinical Implications

The authors describe the system as supporting research on metalloproteins, catalysts, molecular magnets, and interactions between electron and nuclear spins. They also identify potential relevance to methods that use electron polarization to improve nuclear magnetic resonance sensitivity; the supplied material does not report clinical testing or patient outcomes.

Conclusion

The reported 263 GHz EPR system enabled high-sensitivity measurements of manganese in chemical samples and metal-binding proteins without a resonant cavity. The protein spectra distinguished manganese coordination environments, providing measurements relevant to studies of metal-binding biology.

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