4-(2-aminoethyl)benzenesulfonyl fluoride derivatized residue 183.035400390625 183.2299957275390625 A protein modification that is produced by formation of an adduct with 4-(2-aminoethyl)benzenesulfonyl fluoride, AEBS. AEBS AEBSF Aminoethylbenzenesulfonylation C 8 H 9 N 1 O 2 S 1 From DeltaMass: Average Mass: 183 Average Mass Change:183 References:We have found that AEBSF modifies many proteins by covalent attachment, preferentially on Tyr, and to a lesser extent on Lys, His, and the amino-terminus. These modifications were identified by electrospray MS of the proteins (adds 183 Da per AEBS-group) and by peptide mapping and MS/MS. All the proteins we examined were modified after 24 hrs. at 4 C with 1 mM AEBSF in TRIS, pH 8.0. The reaction is 10-20x slower at pH 7; however AEBSF is quite stable in aqueous solution and the extent of to which the protein is modified continues to increase for several days. We have seen the addition of 10 or more AEBS-groups to proteins after prolonged storage. We found no equivalent modification from PMSF, probably because it degrades so quickly. We no longer use AEBSF, and urge caution to those who do. To address the problem, Boehringer Mannheim (now Roche Molecular Biochemicals) introduced Pefabloc PLUS which includes an additional component to compete for these side reactions. In our limited experience with Pefabloc PLUS, it reduces the +183 modifications, but does not always eliminate them. As a result, we prefer PMSF, despite its own set of drawbacks. We have never found PMSF-induced modification of proteins (except trypsin), probably due to its short half-life in aqeous solution. MOD:00596 PSI-MOD Unimod:276 X artifact sulfonyl halide reagent derivatized residue