Table II

Recovery rates and reproducibility of detection of selected phosphopeptides in the enrichment procedure using lactic acid-modified titania MOC tips

Tryptic digests of α-casein, fetuin, and phosvitin (2.5 μg/tip) were purified using lactic acid-modified titania MOC tips. Recovery was calculated based on peak areas in the extracted ion chromatograms of the phosphopeptide-enriched sample and sample without enrichment. Peak intensities were from samples without enrichment. Bold and underlined letters represent identified and ambiguous phosphorylated sites, respectively.

Protein sequenceNo. of phosphorylated sitesChargeRecovery ± S.D. (n = 3)Peak intensity
%
α-Casein S1
    VNELSK125.8 ± 1.52340
    VPQLEIVPNSAEER1298.7 ± 15.16406
    YKVPQLEIVPNSAEER1312.4 ± 3.95982
    DIGSESTEDQAMEDIK22147.5 ± 119.5795
α-Casein S2
    EQLSTSEENSK126.7 ± 0.81250
    EQLSTSEENSKK222.2 ± 0.5610
    NMAINPSK12148.7 ± 13.512303
    TVDMESTEVFTK1294.8 ± 11.13571
Fetuin
    CDSSPDSAEDVRK1330.3 ± 9.6182
    HTFSGVASVESSSGEAFHVGK2341.1 ± 6.31493
Phosvitin
    TTSFPHASAAEGER1378.3 ± 12.76371
    TTSFPHASAAEGER2241.2 ± 11.2965
    TTSFPHASAAEGERSVHEQK3320.5 ± 4.03669