Specificity of NEM toward cysteine residues

Dominique DELFORGE dodel at biocell.fundp.ac.be
Tue Aug 13 10:27:59 EST 1996

In our experiments, we recently used two different cysteine-directed
chemical reagents i.e. 5,5'-dithiobis(2-nitrobenzoic)acid (DTNB) and
N-ethylmaleimide (NEM) in order to determine the possible presence of a
cysteine residue in the active site of L-alanine dehydrogenase. The
results obtained show that the enzyme is not inactivated by DTNB even when
used in large excess relative to the enzyme with long reaction times. On
the other hand, the enzyme is rapidely inactivated by NEM when used in
large excess.

My questions are: Does someone know something about the chemical
specificity of N-ethylmaleimide ? Is this reagent completely specific of
cysteine residues ? When used in large excess, does the reagent react with
other residues than cysteine ? With which residues does it then also react
? Is DTNB more specific (or exclusively specific) of cysteine residues ?
Do you have litterature references about the chemical specificity of NEM ?

Thank you very much for your help !

Dominique DELFORGE
Laboratory of Cellular Biochemistry,
Facultés Universitaires ND de la Paix,
61, rue de Bruxelles,
B-5000 Namur (Belgium).
Fax: ++/32/81/72.41.35.
Phone: ++/32/81/72.41.28

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