Abstract: Saturation transfer effect in NMR experiments on peptide and proteins in aqueous solutions has been investigated using presaturation method with varied irradiation time.The reason why most amide protons are not affected by 60s irradiation has been quantitatively analyzed.It has been shown that the labile protons in lysozyme, which is a macromolecule with stable secondary and tertiary structure, are almost not affected by saturation transfer.Very few amide protons in insulin, whose tertiary structure is less stable than lysozyme, have lost intensity due to saturation transfer.As for the peptide with six amino acid residues, because it dose not have secondary structure in solution, saturation transfer effect is severe.It is thus concluded that for the purpose of three-dimensional structure study using NMR, presaturation is still a powerful and practical technique for solvent suppression.

Key words: Peptide and protein NMR, Presaturation, Saturation transfer effect