Table III

Modified peptides identified from the tryptic digest (listed in elution order)

Ion detectedMH+calculatedStructureΔ[ppm]
418.608(3+)1253.7584K(Ac)APAAAAEKKVK15+40
438.611(3+)1313.7794K(Ac)APAATTEKKVK15+29
341.978(4+)1364.8891Embedded Image(Ac,Me3)APAAAAEKK13a+44
413.773(4+)1652.0111APEmbedded Image(Ac,Me3)APAATTEKKVK15b+35
Me31APKK(Ac)APAATTEKKVK15c
410.269(4+)1637.995Me21APKK(Ac)APAATTEKKVK15d+35
398.770(4+)1591.9901Embedded Image(Ac,Me3)APAAAAEKKVK15a
Me3APEmbedded Image(Ac)APAAAAEKKVK15e+42
395.266(4+)1577.974Me21APEmbedded Image(Ac)APAAAAEKKVK15e+42
487.961(3+)1461.84339VLK(Ac)QVHPDVGISK51+17
631.668(3+)1892.972104HAISEGTK(Me2)AVTKFSSSTN121f+9
104HAISEGTK(Me3)AVTKFSSSSN121
1892.935104HAISEGTK(Ac)AVTKFSSSSN121+28
636.323(3+)g1906.950104HAISEGTK(Me3)AVTKFSSSTN121+2
  • a AcK is present, Me3 is either on K or on the N terminus.

  • b In the CID spectrum of the first eluting peptide internal ions indicate that both Lys residues are modified.

  • c In the CID of the second eluting peptide y14was detected modified by only +42 Da, b3 shows the presence of Me3, and the Lys immonium ion indicates acetylation. The two differently modified species were not separated chromatographically.

  • d Same CID as above, very weak b3present.

  • e From the presence of the 42-modified y14it is obvious that the N terminus is modified. However the first b fragment detected is b4doubly modified.

  • f These structures represent identical masses, the CID spectrum displays y ions from H2B.1, and also features b fragments modified by 42 Da (Fig. 8).

  • g No CID data.