High-sensitivity mass spectrometry for analysis of posttranslational modifications

Pulsed fast atom bombardment ionization (pulsed-FAB) mass spectrometry has been developed to improve the sensitivity of tandem mass spectrometry (MS/MS), allowing it to be used for the analysis of very small samples. MS/MS, when used with a magnetic four-sector instrument coupled with the pulsed-FAB system, allows significant enhancement in product ion intensity of over ten-fold in magnitude over conventional FAB. MS/MS was applied to the structural analysis of a unique nuclear protein, designated p28, which was isolated from a histone fraction obtained from starfish testes, The results clearly show that protein p28 is a heterodimer composed of testicular histones H2B and H4 which are cross-linked between Gln(9) of H2B and Lys(5) of H4.