Figure 2.
Figure 2. a, The zinc binding in the Shaw T1 tetramer. His 75
(layer 3) is shown in red, Cys 102 and Cys 103 are shown in
yellow (layer 4). Cys 81 from the adjacent monomer layer 3, is
shown in black. Distances between Zn^2+ and coordinating atoms
are given. b, X-ray fluorescence spectra were obtained from
single Shaw T1 crystals scanned from 9,200−9,800 eV ( E
= 0.8 eV) with a scintillation counter oriented at right angles
to the beam (BL1-5, Stanford Synchrotron Radiation Laboratory).
The fluorescence intensity was normalized to the flux of the
incident X-ray as measured by an ion chamber. The data were
processed with the program DISCO^39. The values of f" come from
fitting the data to the theoretical absorption curve for Zn in
the regions above and below the Zn K edge. The theoretical value
for the K edge of elemental Zn is 9,659 eV; the observed value
for two separate measurements was found to be about 2 eV higher.
Spectra taken on crystallization buffer and loop, cryoprotectant
and loop, and loop alone did not demonstrate any observable
signal for identical scans (data not shown). X-ray fluorescence
scanning of crystals at wavelengths around the Mn^2+ and Co^2+ K
edges also did not show any signal. Shaw T1 anomalous dispersion
data set was collected at 9,670 eV (1.28 Å). Overall
completeness was 99.9%, and Bijvoet pairs were 67% complete to
1.95 Å. An 8 peak
was located in an anomalous difference Patterson map which
corresponded to the site of the zinc in the monomer. c,
Stereodiagram of (2F[ o] - F[c]) electron density maps of Shaw
T1 superimposed with the final refined model for the region near
the layer 4 in a viewpoint similar to that in (a). Maps are
contoured at 1 .
d, Stereodiagram of (2F[o] - []F[c]) electron density maps of
Shaker T1 superimposed with the final refined model for the
region showing the layers 3 and 4 in the region near the
C-terminus of layer 4. Maps are contoured at 1 .
The above figure is reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Biol
(1999,
6,
38-43)
copyright 1999.
E
= 0.8 eV) with a scintillation counter oriented at right angles
to the beam (BL1-5, Stanford Synchrotron Radiation Laboratory).
The fluorescence intensity was normalized to the flux of the
incident X-ray as measured by an ion chamber. The data were
processed with the program DISCO^39. The values of f" come from
fitting the data to the theoretical absorption curve for Zn in
the regions above and below the Zn K edge. The theoretical value
for the K edge of elemental Zn is 9,659 eV; the observed value
for two separate measurements was found to be about 2 eV higher.
Spectra taken on crystallization buffer and loop, cryoprotectant
and loop, and loop alone did not demonstrate any observable
signal for identical scans (data not shown). X-ray fluorescence
scanning of crystals at wavelengths around the Mn^2+ and Co^2+ K
edges also did not show any signal. Shaw T1 anomalous dispersion
data set was collected at 9,670 eV (1.28 Å). Overall
completeness was 99.9%, and Bijvoet pairs were 67% complete to
1.95 Å. An 8 
peak
was located in an anomalous difference Patterson map which
corresponded to the site of the zinc in the monomer. c,
Stereodiagram of (2F[ o] - F[c]) electron density maps of Shaw
T1 superimposed with the final refined model for the region near
the layer 4 in a viewpoint similar to that in (a). Maps are
contoured at 1 
.