Reactions of a glucosinolate breakdown product (benzyl isothiocyanate) with myoglobin

The interaction of various amounts of benzyl isothiocyanate (benzyl-ITC) with myoglobin is known to lead to the formation of derivatives. These have been characterised by the determination of solubility, free amino group, tryptophan content and chromatographic as well as electrophoretic behaviour. In the range between 2.5 and 125 mg benzyl-ITC/g protein, all properties of the reaction products correlate with the concentration of benzyl-ITC. However, at 250 mg benzyl-ITC/g myoglobin, a rather unexpected low degree of derivatization, as well as atypical chromatographic and electrophoretic behaviour, is observed. The proposed explanation was that conformational changes in the presence of a high concentration of hydrophobic benzyl-ITC made fewer amino groups accessible to the reagent. To test this hypothesis we have run the reaction under denaturing conditions. The results showed that the reaction of myoglobin with high concentrations of benzyl-ITC in the presence of 8 M urea led to a higher degree of derivatization than in the presence of water only. In addition, the Mr distribution of the reaction products was determined by MALDI-TOF-mass spectrometry and the overall degree of derivatization calculated from the spectra.