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lect9 - Uses of NMR 1 NMR is a method of chemical...

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Uses of NMR: 1) NMR is a method of chemical analysis. (Who uses NMR in this way?) 2) NMR is used as a method for medical imaging. (called “MRI”) 3) NMR is used as a method for determining of protein, DNA, RNA structure. (one of only 2 possible methods for doing this)
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Plan for today - 1) Some basic principles of NMR. 2) NMR as a protein (and DNA and RNA) structure determination method.
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Nuclei have mass , nuclei have charge. Some nuclei have a property called “ spin ” or “intrinsic angular momentum”. Define: nuclear spin quantum number “ I magnetic quantum number “ m ”. Nuclei with spin have I > zero.
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frequency Each H in the protein is in a unique magnetic environment, and can absorb (or emit) radio waves of a unique frequency.
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Some simple biochemical applications of NMR.
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Is the protein folded?
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+ Spermidine-spermidine acetyltransferase (SSAT) NMR can be used for enzyme assays + 1 H NMR spectra can show reactants being converted to products confirms activity of the SSAT enzyme (see next page).
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spermine N 1 -acetyl spermidine SSAT SSAT N 1 ,N 12 -diacetyl spermine CoA AcCoA CoA AcCoA
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Next go to structure determination by NMR …..
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Structural information is derived from NMR data (primarily) through measurement of the “Nuclear Overhauser Effect” or “NOE”. NOE = the change in the intensity of the NMR signal of one nucleus when the sample is irradiated with radiowaves at the NMR absorption frequency of another nearby nucleus. The NOE depends on the distance between nuclei.
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One-dimensional NMR spectra are not useful for measuring the NOE in proteins, due to overlap in the 1 H spectra. It was necessary to invent two-dimensional (2-D) NMR to measure the NOE (and hence 1 H- 1 H distances) in proteins.
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Illustrate the 2-D NOE spectrum using asparagine as an example.
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2-D NOE spectrum of a protein with 143 amino acids:
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In summary: The 2-D NOE intensities provide information from which the distance between protons can be derived.
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