Once again, chemical intuition may help. At neutral pH values, sulfate
is going to be present at SO4(2-), whereas phosphate will be present as
H2PO4(-) or HPO4(2-). The hydrogen bond network supporting binding may
be able to offer clues. Sulfate is not likely to have any H-bond
acceptors in its ligand sphere (e.g. no interactions with carbonyl
oxygens or aspartate/glutamate).
Of course, having said that, we did publish a structure in which
bicarbonate has an apparent Glu-O acceptor-acceptor interaction that
makes no sense if you believe the Glu is deprotonated. We concluded that
the Glu residue must be protonated in this structure even as the
solution pH was near neutrality else there would be significant
electrostatic repulsion. (Plus, there was a nice precedent for this
ligand sphere around bicarbonate.)
Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 13346
tel: (315)-228-7245
ofc: (315)-228-7395
fax: (315)-228-7935
email: [email protected]
On 11/11/2016 11:49 AM, Gulcin Gulten wrote:
Similarly, how do you differentiate a phosphate ion than sulfate just
based on electron density if data is not at atomic resolution?
Thanks!
On Fri, Nov 11, 2016 at 3:52 AM, Harry Powell <[email protected]
<mailto:[email protected]>> wrote:
Hi all
Sticking to the first question, if you don't restrict yourself to
_X-ray_ crystallography but use your local neutron source instead,
it should be straightforward (subject to all the normal caveats).
On 10 Nov 2016, at 23:02, Tim Gruene wrote:
Dear JPK,
to answer your first question, at atomic resolution you would
notice a density
difference between N and C. At a little less resolution you might
still
measure difference in bond length.
Regrds,
Tim
On Thursday, November 10, 2016 8:41:43 PM CET Keller, Jacob wrote:
Dear Crystallographers,
I don't think there is any feasible way crystallographically to
distinguish
between nitrate and carbonate or bicarbonate-correct? But that
is not my
main question.
My main question is: given that nitrate and carbonate are both very
important and also very different physiologically, and therefore
they must
be distinguished/recognized by cells, how is this done, since
the ions are
so similar in structure? Is there some aspect of these ions that
differs
dramatically of which I am not aware? What kind of "handles" could a
protein grab onto to distinguish between nitrate and
carbonate/bicarbonate?
JPK
*******************************************
Jacob Pearson Keller, PhD
Research Scientist
HHMI Janelia Research Campus / Looger lab
Phone: (571)209-4000 x3159 <tel:%28571%29209-4000%20x3159>
Email: [email protected]
<mailto:[email protected]><mailto:[email protected]
<mailto:[email protected]>>
*******************************************
--
--
Paul Scherrer Institut
Tim Gruene
- persoenlich -
OFLC/102
CH-5232 Villigen PSI
phone: +41 (0)56 310 5297 <tel:%2B41%20%280%2956%20310%205297>
GPG Key ID = A46BEE1A
Harry
--
Dr Harry Powell
Chairman of International Union of Crystallography Commission on
Crystallographic Computing
Chairman of European Crystallographic Association SIG9
(Crystallographic Computing)
--
Post-Doctoral Research Associate
Texas A&M University
Dept. of Biochemistry and Biophysics
Interdisciplinary Life Sciences Building
301 Old Main Drive, Lab 2138
College Station, Texas 77843
