State of Aromatic Amino Acid Residues in Soybean 11S Globulin Heated in the Presence of N-Ethylmaleimide by Derivative Spectrophotometry

The heating of 11S globulin in the presence of N-ethylmaleimide (NEM) caused changes in the intensities of the second derivative spectra, but scarcely affected the positions of the peaks and troughs.The difference-derivative absorption spectra indicated that half of tyrosine residues burried in native 11S globulin was exposed by heating, but tryptophan residues were hardly done. Furthermore, the tryptophanyl fluorescence spectra gave the same information as that obtained by the difference-derivative absorption spectra. The second derivative spectro-photofluorimetry may be used to discriminate between burried and exposed forms of tryptophan residues in protein depending on solvent polarity. These results suggested that the blocking of sulfhydryl residues on heating caused them to retain a hydrophobic region burried in the protein.