Abstract
Preferential Oxidation of the Methionine Residue near the Active Site of Chymotrypsin
Highlights
The discrepancy is due to the fact that trypsin digestion does not go to completion, and larger peptides containing the active center peptide sequence are present in tryptic digests, e.g. peptides 2A and 2B
Oxidation of methionine to methionine sulfoxide is a mild and convenient method of modifying proteins [13], and it is useful to know which methionine residues in the protein are being oxidized
The alkylated protein can be performic acidoxidized and digested with trypsin and “elastase” to yield methionine peptides from which the amount and position of methionine sulfoxide can be determined. The application of this technique to photo-oxidation at pH 7.2 and hydrogen peroxide oxidation at pH 3.2 has shown that the methionine 3 residues removed from the “active center” serine of chymotrypsin are preferentially oxidized in both cases
Summary
Neumann et al for determination of methionine sulfoxide [13]. C The low values of methionine sulfone indicate almost complete alkylation of mcthionines in the control. Neumann et al [13] for determination of methionine sulf oxide. There is appreciable radioactivity in Region 3 on electrophoresis of tryptic digest,s of alkylated, hydrogen peroxide-oxidized chymotrypsin. This should indicate the presence of native chymotrypsin. It has been shown (Table IV) with r4C-iodoacetic acid that essentially all of Met-3 is oxidized. The mono-14C-methylcarboxamide derivatives of these peptides appear in Region 3 on electrophoresis at pH
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