The Thiocarbamate Method

Another method for the stepwise degradation of a polypeptide chain has been suggested by Levy (1950). Here the A-terminal residue is split off as a 2-thiothiazolid-5-one derivative as follows  

Here again the process may be repeated on the peptide chain containing one residue less. This method has not yet been worked out on a small scale, but was found to give satisfactory results with synthetic peptides. 

The reaction of CS2 with amino groups has also been used by L onis (1948) as the basis for a titration method for estimating the total a-amino groups as well as -amino, imino, and thiol groups. CS2 reacts about ten times as rapidly with a-amino groups as with -amino groups, so that the two may be distinguished. 

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