Spectroscopic and protein chemical analyses demonstrate the presence of C-mannosylated tryptophan in intact human RNase 2 and its isoforms

Mass spectrometric and nuclear magnetic resonance spectroscopic studies were performed on human urinary RNase 2 and its peptides at a pH of less than five. In addition, the effect of acidic conditions on the biosynthesis of the glycopeptide F(O3-Man-)TWA was examined. The results indicated that the C-mannosylation of Trp-7 in RNase 2 was not caused by the acidic conditions used in the isolation and purification of the enzyme and its peptides. In addition, RNase from erythrocites were also found to contain (C2-Man-)Trp.