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. Author manuscript; available in PMC: 2017 Apr 15.
Published in final edited form as: Mol Cell Endocrinol. 2015 Dec 28;425:48–60. doi: 10.1016/j.mce.2015.12.006

Figure 1. MRM spectra of synthetic IGFBP-1 peptides used for CK2 in vitro kinase assay.

Figure 1

MRM/MS analysis of phosphorylation of Ser residues (S) on IGFBP-1 peptides, non-phosphorylated synthetic peptides were used as substrates for CK2 enzyme. Following incubation, CK2-induced phosphorylation of each peptide was then monitored by targeting the phosphorylation-specific version of each IGFBP-1 peptide substrate by MRM-MS using a QTRAP 4000 mass spectrometer. CK2 phosphorylates IGFBP-1 at Ser101, Ser119 and Ser169. Ser101 was found to be doubly phosphorylated with Ser98, and Ser169 was indicated to be doubly phosphorylated with Ser174.