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. 2016 Apr 29;291(27):14185–14198. doi: 10.1074/jbc.M116.718197

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© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

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FIGURE 10. — Mass spectra of products derived from the K-Ras4b reporter treated with purified SmSte24p. A–C, samples of K-Ras4b reporter incubated in the absence (A) and presence of purified SmSte24p (B and C) were analyzed by LC-MS using a Bruker Esquire 3000 Plus mass spectrometer. The sequences and theoretical masses that correspond to identified peaks are shown centered or adjacent to appropriate peaks. One of the prenylated species in A lacking ABZ and N-terminal Lys (SKTKC(f)VIK^D) is probably a minor impurity from peptide synthesis. Spectra for B and C were derived from different LC fractions corresponding to 19.7–20 min and 20.2–20.4 min, respectively. D and E, the non-prenylated species detected in A was not present in mass spectra provided by the peptide manufacturer; they are probably a by-product of ionization (67). In support of this, we observed that MS/MS analysis of the double ion form of the uncleaved farnesylated peptide (m/z 762.4) resulted in the loss of farnesylated peptide ions (MH⁺, m/z 1523.9; MH₂²⁺, m/z 762.4 m/z) (D) and the appearance of non-prenylated peptide ions (MH⁺, m/z 1319.8; MH₂²⁺, m/z 660.4) (E).

FIGURE 10. — Mass spectra of products derived from the K-Ras4b reporter treated with purified SmSte24p. A–C, samples of K-Ras4b reporter incubated in the absence (A) and presence of purified SmSte24p (B and C) were analyzed by LC-MS using a Bruker Esquire 3000 Plus mass spectrometer. The sequences and theoretical masses that correspond to identified peaks are shown centered or adjacent to appropriate peaks. One of the prenylated species in A lacking ABZ and N-terminal Lys (SKTKC(f)VIK^D) is probably a minor impurity from peptide synthesis. Spectra for B and C were derived from different LC fractions corresponding to 19.7–20 min and 20.2–20.4 min, respectively. D and E, the non-prenylated species detected in A was not present in mass spectra provided by the peptide manufacturer; they are probably a by-product of ionization (67). In support of this, we observed that MS/MS analysis of the double ion form of the uncleaved farnesylated peptide (m/z 762.4) resulted in the loss of farnesylated peptide ions (MH⁺, m/z 1523.9; MH₂²⁺, m/z 762.4 m/z) (D) and the appearance of non-prenylated peptide ions (MH⁺, m/z 1319.8; MH₂²⁺, m/z 660.4) (E).