muramidase and 2-aminothiophenol

Jones et al. have reported that the epsilon-carbons of methionine residues in myoglobin can be enriched with stable isotope (13C) in two steps, i.e., methylation of methionine residues with 13CH3I in the protein and thiolysis using dithiothreitol [Jones, W.C., Rothgeb, T.M., and Gurd, F.R.N. (1976) J. Biol. Chem. 251,7452-7460]. Using their method, we failed to prepare active lysozyme in which the epsilon-carbons of methionine residues are enriched with 13C, because many side reactions took place under the thiolysis condition (pH 10.5, 37 degrees C). When we employed 2-aminothiophenol as a reagent for thiolysis, the reduction proceeded under a weakly acidic condition to afford fully active lysozyme, in which the epsilon-carbons of two methionine residues were enriched with 13C, in a 30% yield. Analysis of the 13C-edited NOESY spectra of 13C-enriched methionine lysozyme in the absence and presence of a substrate analogue indicated the occurrence of conformational change around Met 105 in lysozyme.

Topics: Aniline Compounds; Binding Sites; Carbon Isotopes; Isotope Labeling; Methionine; Methylation; Muramidase; Nuclear Magnetic Resonance, Biomolecular; Protein Conformation; Sulfhydryl Compounds

We developed a method for reducing disulfide bonds in proteins under weakly acidic conditions by use of 2-aminothiophenol. The disulfide bonds in hen egg-white lysozyme, ribonuclease A, and soybean trypsin inhibitor were quantitatively reduced by 2-aminothiophenol in phosphate buffer, pH6, containing 8 M Gdn HCl, 1 mM EDTA, and 20% ethanol, for 60 min at 40 degrees C. On analysis of the RP-HPLC patterns of tryptic peptides, which were derived from reduced and S-alkylated lysozyme and ribonuclease A at pH 6, it was confirmed that no side reaction occurred. Moreover, the reduction under weakly acidic conditions was demonstrated to be applicable for the location of such a labile residue as O-acetylated tyrosine.

Topics: Aniline Compounds; Animals; Chickens; Cysteine; Disulfides; Hydrogen-Ion Concentration; Muramidase; Oxidation-Reduction; Proteins; Succinimides; Trypsin