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Determination of the Distance Between Two Spin Labels Attached to a Macromolecule

Mark D. Rabenstein and Yeon-Kyun Shin
Proceedings of the National Academy of Sciences of the United States of America
Vol. 92, No. 18 (Aug. 29, 1995), pp. 8239-8243
Stable URL: http://www.jstor.org/stable/2368033
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Determination of the Distance Between Two Spin Labels Attached to a Macromolecule
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Abstract

An EPR "spectroscopic ruler" was developed using a series of α-helical polypeptides, each modified with two nitroxide spin labels. The EPR line broadening due to electron-electron dipolar interactions in the frozen state was determined using the Fourier deconvolution method. These dipolar spectra were then used to estimate the distances between the two nitroxides separated by 8-25 Å. Results agreed well with a simple α-helical model. The standard deviation from the model system was 0.9 Å in the range of 8-25 Å. This technique is applicable to complex systems such as membrane receptors and channels, which are difficult to access with high-resolution NMR or x-ray crystallography, and is expected to be particularly useful for systems for which optical methods are hampered by the presence of light-interfering membranes or chromophores.

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