Saturation Transfer Spectroscopy of Biological Membranes

Non-adiabatic rapid passage (NARS) electron paramagnetic resonance (EPR) spectroscopy was introduced by Kittell, A.W., Camenisch, T.G., Ratke, J.J. Sidabras, J.W., Hyde, J.S., 2011 as a general purpose technique to collect the pure absorption response. The technique has been used to improve sensitivity relative to sinusoidal magnetic field modulation, increase the range of inter-spin distances that can be measured under near physiological conditions, and enhance spectral resolution in copper (II) spectra. In the present work, the method is extended to CW microwave power saturation of spin-labeled T4 Lysozyme (T4L). As in the cited papers, rapid triangular sweep of the polarizing magnetic field was superimposed on slow sweep across the spectrum. Adiabatic rapid passage (ARP) effects were encountered in samples undergoing very slow rotational diffusion as the triangular magnetic field sweep rate was increased. The paper reports results of variation of experimental parameters at the interface of adiabatic and non-adiabatic rapid sweep conditions. Comparison of the forward (up) and reverse (down) triangular sweeps is shown to be a good indicator of the presence of rapid passage effects. Spectral turning points can be distinguished from spectral regions between turning points in two ways: differential microwave power saturation and differential passage effects. Oxygen accessibility data are shown under NARS conditions that appear similar to conventional field modulation data. However, the sensitivity is much higher, permitting, in principle, experiments at substantially lower protein concentrations. Spectral displays were obtained that appear sensitive to rotational diffusion in the range of rotational correlation times of 10−3 to 10−7 s in a manner that is analogous to saturation transfer spectroscopy.

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“…It has been extensively used to study slow rotational diffusion. Reviews were provided by Beth [15] and by Marsh [16]. …”

Section: Introductionmentioning

confidence: 99%

Spin-label CW microwave power saturation and rapid passage with triangular non-adiabatic rapid sweep (NARS) and adiabatic rapid passage (ARP) EPR spectroscopy

Kittell

Hyde

2015

Journal of Magnetic Resonance

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“…In the limit of low modulation amplitude the 1 st harmonic is a good approximation of the first-derivative EPR signal. The 2 nd harmonic (second derivative) has been found to be informative for resolution enhancement [10–12] and for saturation transfer EPR [13]. Higher harmonics have not been recorded for two reasons: (i) low S/N, and (ii) if phase sensitive detection (PSD) is done in hardware, detection of each harmonic would require a separate phase shifter, video amplifier, and digitizer channel.…”

Section: Introductionmentioning

confidence: 99%

Reconstruction of the first-derivative EPR spectrum from multiple harmonics of the field-modulated continuous wave signal

Tseitlin

Eaton

2011

Journal of Magnetic Resonance

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Selection of the amplitude of magnetic field modulation for continuous wave electron paramagnetic resonance (EPR) often is a trade-off between sensitivity and resolution. Increasing the modulation amplitude improves the signal-to-noise ratio, S/N, at the expense of broadening the signal. Combining information from multiple harmonics of the field-modulated signal is proposed as a method to obtain the first derivative spectrum with minimal broadening and improved signal-to-noise. The harmonics are obtained by digital phase-sensitive detection of the signal at the modulation frequency and its integer multiples. Reconstruction of the first derivative EPR line is done in the Fourier conjugate domain where each harmonic can be represented as the product of the Fourier transform of the 1st derivative signal with an analytical function. The analytical function for each harmonic can be viewed as a filter. The Fourier transform of the 1st derivative spectrum can be calculated from all available harmonics by solving an optimization problem with the goal of maximizing the S/N. Inverse Fourier transformation of the result produces the 1st derivative EPR line in the magnetic field domain. The use of modulation amplitude greater than linewidth improves the S/N, but does not broaden the reconstructed spectrum. The method works for an arbitrary EPR line shape, but is limited to the case when magnetization instantaneously follows the modulation field, which is known as the adiabatic approximation.

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“…39, 44, and 45 showed the community how to use the effect of motion on the line shapes of spin labels to monitor the uncoiling of a protein, the binding of a nitrophenyl group to an antibody, and changes in membrane structure and dynamics upon other species interacting with the membrane. Spin label and spin probe studies have become major fields, encompassing fundamental studies of molecular motion (33), detailed structure of membranes (33)(34)(35)(36)(37), distance measurements (38), fundamental studies of electron spin relaxation in small molecules (39), and many other biomolecular problems. Special attention should be paid to the power of site-directed spin labeling, by which a spin label can be put at a selected position in a protein (36,40).…”

Section: Nitroxyl Radical Spin Probes and Spin Labelsmentioning

confidence: 99%

EPR at work: Part 1

Hyde

2006

Concepts Magnetic Resonance

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Saturation Transfer Spectroscopy of Biological Membranes

Cited by 8 publications

References 61 publications

Spin-label CW microwave power saturation and rapid passage with triangular non-adiabatic rapid sweep (NARS) and adiabatic rapid passage (ARP) EPR spectroscopy

Spin-label CW microwave power saturation and rapid passage with triangular non-adiabatic rapid sweep (NARS) and adiabatic rapid passage (ARP) EPR spectroscopy

Reconstruction of the first-derivative EPR spectrum from multiple harmonics of the field-modulated continuous wave signal

EPR at work: Part 1

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