th  - 1988 - 51st ENC Conference

21 DETECTION OF LONG-RANGE IH-19F COUPLINGS USING A HETERONUCLEAR
[ EQUIVALENT OF THE COSY PULSE SEQUENCE.
Donald W.Hughes and Alex D.Bain, Department of Chemistry, McMaster University,
Hamilton, Ontario. Canada. LSS 4MI.
Heteronuclear chemical shift correlation has become an indispensable technique for
assigning the spectra of natural products. The original pulse sequence (I)
IH : D1 - 90 ° - t I - 90 °
X : 90 ° - ACQ
has been largely neglected by spectroscopists because of the complications arising from
heteronuclear coupling in both dimensions. Recently this pulse sequence was reexamined
with a phase-sensitive modification (2). The principle advantage this heteronuclear
correlation (HETCOSY) method is that like the homonuclear COSY experiment it is a
robust technique i.e.resistant to errors. HETCOSY can produce correlations between
protons and X nuclei without prior knowledge of X-IH coupling constants. This feature
makes HETCOSY useful for establishing correlations between protons and X nuclei such
as 19F and 31p, especially in cases where the X-IH couplings are not well resolved. The
present study deals with the application of HETCOSY in identifying which fluorine
nuclei are responsible for long-range IH-19F couplings in corticosteriods related
to fluocinonide.
I. A.A.Maudsley and R.R. Ernst. Chem. Phys. Lett.50, 368 (1977)
2. A.D. Bain. J. Magn. Reson. In press (1988)
I -- 22 I
STUDIES OF PHOSPHORYLATED SITES IN PROTEINS USING IH -
David H. Live and Dale E. Edmondson #
31p
2-DIMENSIONAL NMR
*Department of Chemistry and #Department of Biochemistry, Emory University,
Atlanta, GA 30322
The application of proton detected IH - 31p multiquantum 2-dimensional
NMR to directly studying the phophorylated sites of proteins is demonstrated
here. This approach works well for proteins up to molecular weight of about 40
kD in spite of the fact ~at the 2D spectrum is mediated by small 3 or more
bond couplings between ~P and protons on phosphorylated amino acid residues.
Results are presented for the protein Azotobacter flavodoxin, an electron
carrier in nitrogen fixation. The results provide the first direct evidence
for the existence of a phosphate diester linkage between a seryl and a
threonyl residue in the protein. Data from this protein are compared to that
from phosphoserine, phosphothreonine and ovalbumin.
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