Abstract
Treatment of amino acids, peptides, and proteins with aqueous solution of dimethyl sulfoxide (Me2SO) and hydrochloric acid (HCl) resulted in the oxidation of methionine to methionine sulfoxide. In addition to methionine, SH groups are also oxidized, but this reaction proceeds after a lag period of 2 h. Other amino acids are not modified by aqueous Me2SO/HCl. The reaction is strongly pH-dependent. Optimal conditions are 1.0 M HCl, 0.1 M Me2SO, at 22 degrees C. The reaction exhibits pseudo-first order kinetics with Kobs = 0.23 +/- 0.015 M-1 min-1 at 22 degrees C. Incubation of methionine sulfoxide with dimethyl sulfide and HCl resulted in the conversion of methionine sulfoxide to methionine. This reaction is fast (t1/2 = 4 min at room temperature) and quantitative at relatively anhydrous condition (i.e. at H2O:concentrated HCl:dimethyl sulfide ratio of 2:20:1). Quantitative conversions of methionine sulfoxide back to methionine are obtained in peptides and proteins as well, with no observable other side reactions in amino acids and proteins. The wide applications of this selective oxidation and reduction of methionine residues are demonstrated and discussed.
Highlights
Action proceedsafter a lag period of2 h
0.015 M” min” at 22 “C.Incubationofmethionine sulfoxide with dimethyl sulfide and hydrochloric acid (HCl) resulted in the conversion of methioninseulfoxide to methionine
Conditions and reagents which are highly selective in the Materials-Bovine a-lactalbumin, ribonuclease, insulin, adrenocorticotropic hormone (ACTH), methionine sulfoxide,5,5’-dithiobismodification of certain amino acids in peptides and proteins 8-nitrobenzoic acid), and chloramine-T were purchased from Sigma
Summary
Conditions and reagents which are highly selective in the Materials-Bovine a-lactalbumin, ribonuclease, insulin, adrenocorticotropic hormone (ACTH), methionine sulfoxide,5,5’-dithiobismodification of certain amino acids in peptides and proteins 8-nitrobenzoic acid), and chloramine-T were purchased from Sigma. The chlorosuccinimide,at neutral orslightly alkaline pH, will only derivative, 1-MetO-a-lactalbumin, was prepared by allowing a-lacoxidize methionine residues to methionine sulfoxide, in nonSH containing proteins [2]. These mild chlorinating agents were by far more suitable to this purpose since other previously used conditions and reagents such as periodate [3, 4], talbumin (20 mg in 10 ml of 0.1 M Tris-HC1 buffer, pH 8.4) to react with 10 M excess of chloramine-T for 1h at room temperature. The protein solution was extensively dialyzedand lyophilized In this derivative, the single methionyl residue of a-lactalbumin of bovine milk is oxidized to methionine sulfoxide. Rat fat cells were prepared according to Rodbell [25]
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