[Direct incorporation of 18O isotopes into peptides and proteins for quantative analysis by mass spectrometry method].

The method of direct introduction 18O isotopes in peptides and proteins carboxylic groups through the exchange with H218O in the presence of TFA is shown. The isotope label is steady enough in awide range of pH. Because the labeled compounds retain their physical and chemical characteristics, they can be used as an internal standard in quantitative determination of authentic compounds in the analyzed sites by mass spectrometry methods. The technique may be applicable for quantitative analysis of peptides and proteins in biological environments, for quantitative study of the kinetics of metabolism and enzymatic activity. For polypeptides and proteins the quantitative analysis is combined with trypsinolysis. If necessary, the isotope label may be introduced simultaneously in all peptides and proteins control bioassays, making it suitable for use as a standard for the comparative analysis of experimental bioassays.

[MALD-MS in the quantitative analysis of peptides and proteins]. / Ispol'zovanie MALDI-MS dlia kolichestvennogo analiza peptidov i belkov.

A modified method of isotope dilution was applied to the quantitative determination of peptides and proteins by MALDI MS at subpicomolar level. The essence of the method consists in the quantitative analysis of the enzymic hydrolysis products rather than the starting compounds. This allows the measurements to be performed at a higher resolution and makes the method independent of the molecular mass of oligopeptides and proteins examined. Fragments obtained by hydrolysis of the same oligopeptide or protein in a known concentration by the same enzyme and labeled with the stable 18O isotope are used as internal standards. The label is introduced by carrying out the hydrolysis in H(2)18O, and the oligopeptide concentration is calculated from the isotope distribution between the labeled and unlabeled hydrolysis products in the mass spectrum. This method was tested in the determination of concentrations of the angiotensinogen (1-14) fragment (oligopeptide), extracellular RNAase from Bacillus amyloliquefaciens (protein) and its protein inhibitor, barstar M. Usefulness of this method in kinetic studies was also demonstrated.