Table

Overview of observed phosphorylated peptides derived by tryptic digestion of ovalbumin (Ov), α-casein S1 (α-S1) and S2 (α-S2), and β-casein (β-C)

The phosphorylation sites are underlined, and the amino acid position numbers are given in parentheses.

Peptide sequenceNumber of phosphate groups(M + H)+
Da
EVVGSAEAGVDAA (Ov-(340–352))a11254.52
EQLSTSEENSK (α-S2-(141–151))11331.53
EQLSTSEENSK (α-S2-(141–151))21411.50
TVDMESTEVFTK (α-S2-(153–164))11466.61
TVDMESTEVFTKK (α-S2-(153–165))11594.70
VPQLEIVPNSAEER (α-S1-(121–134))11660.79
YLGEYLIVPNSAEER (α-S1)b11832.83
DIGSESTEDQAMEDIK (α-S1-(58–73))11847.69
DIGSESTEDQAMEDIK (α-S1-(58–73))21927.69
YKVPQLEIVPNSAEER (α-S1-(119–134))11951.95
FQSEEQQQTEDELQDK (β-C-(33–48))12061.83
EVVGSAEAGVDAASVSEEFR (Ov-(340–359))12088.89
NVPGEIVESLSSSEESITR (β-C-(7–25))c42352.85
NTMEHVSSSEESIISQETYK (α-S2-(17–36))42619.04
VNELSKDIGSESTEDQAMEDIK (α-S1-(52–73))32678.01
QMEAESISSSEEIVPNSVEAQK (α-S1-(74–94))52720.91
NTMEHVSSSEESIISQETYKQ (α-S2-(17–37))d42747.10
EKVNELSKDIGSESTEDQAMEDIK (α-S1-(50–73))32935.15
ELEELNVPGEIVESLSSSEESITR (β-C-(17–40))42966.16
NANEEEYSIGSSSEESAEVATEEVK (α-S2-(61–85))43008.01
NANEEEYSIGSSSEESAEVATEEVK (α-S2-(61–85))53087.99
RELEELNVPGEIVESLSSSEESITR (β-C-(16–40))43122.27
KNTMEHVSSSEESIISQETYKQEK (α-S2-(16–39))c43132.20
  • a Unusual cleavage (sequence was verified by MALDI tandem MS).

  • b The peptide signal at m/z 1832.8 represents a new sequence variant of the α-S1 casein in the region 104–119 corresponding to the sequence YLGEYLIVPNpSAEER (where pS is phosphoserine) in contrast to the published sequence 104YKVPQLEIVPNpSAEER119. This sequence could originate from an alternative splicing. The sequence was verified by MALDI tandem MS.

  • c Chymotryptic cleavage (sequence was verified by MALDI tandem MS).

  • d Sequence partly verified by MALDI tandem MS. Trypsin indicates Lys instead of Gln in the C terminus.