PLASMA DESORPTION MASS-SPECTROMETRY OF PROTEINS TRANSFERRED FROM GELS AFTER SODIUM DODECYL-SULFATE POLYACRYLAMIDE-GEL ELECTROPHORESIS

It is demonstrated that electroblotting as well as electro-elution allows transfer of proteins from sodium dodecyl sulphate-polyacrylamide gels to the nitrocellulose target used in plasma desorption mass spectrometry (PDMS). The losses in the different procedures are determined using radioactively labelled human insulin and the procedures optimized to minimize losses. In spite of the fact that only a minor fraction of the protein originally applied on the gel after transfer is available for mass spectrometric analysis, both techniques are demonstrated to yield acceptable spectra for different proteins in the molecular weight range 5000-14000. In two-dimensional electrophoresis the sample amount is too small for direct electroblotting, but electro-elution of spots excised from a number of gels followed by PDMS analysis allowed molecular weight determination of a protein from Locusta migratoria, obtained after two-dimensional polyacrylamide gel electrophoresis of the complete cuticle protein mixture.