Fig. 4.

Phosphorylation analysis of selected proteins of PTP1B wild-type and KO cells using quantitative MS and Western blotting. A, selected MS spectra of Tyr(P) peptides depicted in Table I are shown here. All MS spectra were evaluated with MSQuant software. Isotope clusters of Tyr(P) peptides derived from wild-type and KO cells are indicated by braces. For quantitation, only monoisotopic peaks were used; they are marked with corresponding m/z values. B, tyrosine phosphorylated proteins of unstimulated cells were immunoprecipitated with anti-Tyr(P) 4G10 antibodies and separated using SDS-PAGE. Immunoprecipitated proteins were probed with the indicated antibodies. In addition, cellular protein expression levels were analyzed by loading whole cell lysates (right panel). IP, immunoprecipitation; pTyr, phosphotyrosine; wt, wild type; pY, phosphotyrosine; pS, phosphoserine; pT, phosphothreonine; IB, immunoblot.