3JHAHB
KARPLUS
Pairs of 3JHA-HB coupling constants are critical to the
stereospecific resonance assignment of CB-methylene protons.
Empirical 3JHN-HA values and
angular backbone
constraints can be interconverted following well-known Karplus relationships:
3JHA-HB=9.5*cos2(fi) - 1.6*cos(fi) + 1.8
(
99JACS11821
)
VALUES
Examples found in the bibliography: lysozyme (
91BIO986
).
MEASUREMENT
The most simple way to measure this coupling constant in unlabeled
porteins is fitting
the antiphase cross-peak pattern of a phase-sensitive 2D COSY-DQF
spectrum to an specific linewidth. However, because the linewidths
of large proteins are largely in excess of 4-5 Hz and frequently comparable to
1H-1H coupling constants, accurate values are better measured from
E.COSY cross-peaks
(
85JACS6394
).
Other alternatives to be applied on labeled proteins are:
- J-quantitative method
- E.COSY method
-
soft HCCH-E.COSY experiment
(
92JB583
and
94BIO5481
)
- CCH-E.COSY experiment using 13C isotropic mixing
for 13C-13C transfer
polarization
(
92JACS354
).
-
93JMRA321-105
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