ISSN:
0951-4198
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Physics
Notes:
Sarafotoxins (SRTXs) form a family of toxic and potent vasoconstrictor peptides of 21 amino acids and two disulfide bonds. They are present in the venom of the burrowing asp Atractaspis engaddensis. We have made two derivatives of the amino acid sequence of SRTX-b, one of the most potent isotoxins, in the solid phase. First, we replaced Ser2 by Thr, to investigate whether, as previously postulated, this change is responsible for the weak activities of SRTXs c and d. Secondly, we replaced Ser2, Asp18 and Val19 respectively by Thr, Gly and He, with a view to generating SRTX-e whose amino acid sequence was deduced from cDNA.Solid-phase peptide synthesis (SPPS) was performed according to the tert-butyloxycarbonyl strategy and the disulfides were paired sequentially using a selective chemistry. The disulfide 1-15 was formed by oxidation of cysteines1,15 with ferricyanide, whereas disulfide 3-11 was made by iodine oxidation of Acm-blocked cysteines3,11. By plasma desorption mass spectrometry (PDMS), we monitored all possible side reactions that occurred during the synthesis. We thus observed a benzyl shift in mass spectra when aspartic and glutamic acid side chains were protected by a benzyl group during the SPPS. This could be circumvented by using instead, a cyclohexyl protecting group. We also noted the oxidation of the methionine and the tryptophan side chain (formation of methionine sulfoxide and oxindole ring of tryptophan) to a small extent during the cleavage peptide/solid phase oxidation of the methionine side chain during the formation of the disulfide 1-15 by ferricyanide. These known side reactions could be avoided by using a mixture of scavengers (ethanedithiol, dimethylsulfide, thioanisole, m-cresol and skatole) and by shortening the ferricyanide oxidation time to one hour. The sequential disulfied bond formation starting from the linear peptide (mono-disulfied and bi-disulfide) was also monitored by PDMS. PDMS therefore proved to be a sensitive analytical method for the measurement of the molecular weights of synthetic or natural peptides (SRTX peptides in this application) in the field of peptide and protein chemistry.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/rcm.1290081213
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