th  - 1988 - 51st ENC Conference

$8 I
MEASUREMENT OF T I RELAXATION RATES OF COUPLED SPINS VIA 2D ACCORDION
SPECTROSCOPY WITH APPLICATION TO ACYL CARRIER PROTEIN
Lewis E. Kay*, Anne F. Frederick*, and James H. Prestegard
Department of Chemistry, Yale University, New Haven, CT 06511
Nuclear magnetic resonance spectroscopy (NMR) is widely recognized as
a useful technique for probing dynamic and structural properties of
macromolecules. Analysis is most commonly approached through measurements
of NOE spectra. However, the same I/r 6 distance dependence that makes NOE
spectra useful in assessing structure enters into spin-lattice or T 1
relaxation times. In principle, T 1 recoveries can be used for structural
analyses. Application of conventional ID NMR techniques or use of
information on the diagonal in 2D experiments is often impossible due to
lack of spectral resolution, and recently proposed combinations of
inversion recovery experiments with two dimensional COSY detection (IR-
COSY) are very time consuming.
We have developed a pulse sequence based on the accordion experiment,
which provides a framework for the reduction of the time consuming three
dimensional IR-COSY experiment to a more practical 2D experiment. We will
present applications of this sequence to the measurement of IH TlS in Acyl
Carrier Protein (ACP), a small protein of molecular weight 8800 D. IH TlS
obtained from a sample of ACP in the absence of metal and in the presence
of Mn 2+ have been used as constraints in molecular mechanics calculations
in order to locate the metal binding sites in this protein.
59 UNTRUNCATIO.~I OF DIPOLE-DIPOLE COUPLINGS IN SOLIDS, OR ZEP, O FIELD
I NMR ENTIRELY IN HIGH FIELD. Robert Tycko, AT&T Bell Laboratories,
Murray Hill, NJ, 07974.
N;:R spectra of powdered or noncrystalline solids in high field commonly exhibit broad
lines that arise from the dependence of the nuclear magnetic dipole-dipole couplings
on molecular orientation. New experiments will be described in which that orientation
dependence is removed by the combination of rapid sample rotation with a synchronized
rf pulse sequence. The sample rotation and pulse sequence have the effect of con-
verting the usual truncated dipole-dipole couplings into an untruncated form. The
result is N~IR spectra with sharp lines and splittings that depend only on inter-
nuclear distances, i.e. spectra with a "zero field" appearance that are obtained
entirely in high field. Such spectra provide a means of studying molecular conforma-
tions in solids without requiring single crystals. The theory behind untruncation
experiments will be presented along with experimental spectra of simple organic
solids.
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