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. Author manuscript; available in PMC: 2009 Apr 2.
Published in final edited form as: Biochemistry. 2008 Dec 30;47(52):14009–14019. doi: 10.1021/bi801392j

Figure 4.

Figure 4

Tandem quadrupole product ion spectra of the [M − H]− ions at m/z 425 arising from SS425 (a) and the cort21S standard (b). The two spectra are identical, indicating that the ion seen at m/z 425 from endogenous sample is cort21S. The IT MS2 spectrum of the [M − H]− ions at m/z 425 from SS425 (c) is also identical to that arising from the synthetic standard (not shown). The mass shifts of the analogous ions seen in the tandem quadrupole product ion spectra of the [M − H]− ions at m/z 427 from a 34S-containing isomer (d) and at m/z 426 from a 2H-containing isomer (e) and the IT MS2 spectrum of the ion at m/z 427 from a 34S-containing isomer (f) are in accordance with the proposed fragmentation processes that are depicted in Scheme 2.