Specificity of NEM toward cysteine residues

[Michael Galperin]

>malexe at biost1.thi.tmc.edu (Mikhail Alexeyev) writes:
>>dodel at biocell.fundp.ac.be (Dominique DELFORGE) wrote:

>> 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 ?
>> 
	As far as I recall, N-EM can alkylate His and, at certain pH, even 
other residues (Lys?). Anyway, effect of N-EM is by no means a proof of the
presence of a thiol residue in the active center.
As for references, I would start with "Enzyme Inhibitors" by E. C. Webb
Also, you could look in Meth. Enzymol. 25, 449 (1972).

Michael Galperin                        galperin at biotek.mcb.uconn.edu