disulphide location in short peptides

[Gurmil Singh s/o Dalip Singh]

Dear Netters,

I am currently working on the secondary structure of a short peptide of 
35 amino acids. It got 6 Cys and all are involved in disulphide bonds 
i.e. 3 of them. I am trying to digest my peptide in the un-reduced form 
in order to determine the location of the disulphides, however, none of 
the enzymes I have used seems to work. These include Glu-C, Lys-C, 
Chymotrypsin, Trypsin and Pepsin. Stringent denaturing treatment of the 
peptide prior to digestion i.e. 8 M Urea or 6 M Guanidine-HCl proof to be 
ineffective as well. Any suggestions on how I can get around this problem 
and get my disulphide location will be most welcomed.

Gurmil Gendeh
medp4044 at leonis.nus.sg