Parveen,
Bert and Pascal are correct in that most alkyl glycoside detergent are
notoriously difficult to crystallize in aqueous solution when you have
the beta-anomer (what we normally buy). However, the alpha-anomers
can be quite easy to crystallize and can contaminate batches of beta-
alkyl glycoside detergents. While the quality control procedures are
usually good enough to ensure that the alpha-anomer contamination of
DDM, DM, and OG are low, it may not be low enough for all
crystallization experiments. Twenty or so years ago, I was even shown
a batch of "pure" beta-OG from a company I shall not name which was
insoluble in water.
Some people have complained about this, but the impact of alpha-anomer
contamination on crystal growth and spurious detergent crystallization
is unknown. If this persists and you are sure that those are
detergent crystals, you might ask to see information about alpha-
anomer contamination for your batch of detergent. Companies like
Anatrace will be quite forthcoming with information, but larger
companies (Sigma or Rohm & Haas) may give you the run around.
Good luck,
Michael
****************************************************************
R. Michael Garavito, Ph.D.
Professor of Biochemistry & Molecular Biology
513 Biochemistry Bldg.
Michigan State University
East Lansing, MI 48824-1319
Office: (517) 355-9724 Lab: (517) 353-9125
FAX: (517) 353-9334 Email: garav...@msu.edu
****************************************************************
On Aug 4, 2009, at 12:51 PM, Van Den Berg, Bert wrote:
Hi Jose,
how do you know that those crystals were detergent and not protein?
My impression is that it is really hard to crystallize DDM, and even
harder for DM (solubilities > 20% in water). The easiest (?) way to
check this may be to take some crystals, wash them well and run them
out on a PAGE gel. If you don't see anything and you've taken enough
crystals, then you're probably dealing with pure detergent crystals.
As for your second point, you're right. For most low-cmc detergents
the total detergent concentration will be substantially higher than
reported, since a substantial amount is always bound to your
protein. For 1 mM DDM, you would have only ~ 20 uM micelles,
assuming an aggregation # of 50 (its higher). I don't think people
measure the total detergent concentration in the end; for maltosides
one could in principle do a Fehling's based assay to get the
concentration.
Cheers, Bert
Bert van den Berg
University of Massachusetts Medical School
Program in Molecular Medicine
Biotech II, 373 Plantation Street, Suite 115
Worcester MA 01605
Phone: 508 856 1201 (office); 508 856 1211 (lab)
e-mail: bert.vandenb...@umassmed.edu
http://www.umassmed.edu/pmm/faculty/vandenberg.cfm
"Parveen Goyal" wrote:
> Hi All,
>
> I got some hexagonal crystals in one of my crystal condition. The
protein is
> a membrane protein and contains 0.05% DDM. Has anybody seen DDM
crysals
> and > if yes, how do they look like?
>
> thanks in advance
>
> Parveen Goyal
>
