Figure 2. Mass spectra for the long-wavelength sensitive cone opsin, which increased in abundance during thyroid hormone treatment

A: Time-of-flight MS spectrum of isotope-coded affinity tag (ICAT) labeled peptides including light (D0) and heavy (D9) versions of the ICAT molecule. The difference in abundance between these peaks indicated that long-wavelength sensitive (LWS) opsin was 1.9 fold more abundant in the peptide pool from thyroid hormone-treated retinas, which was labeled with the heavy isotope of the ICAT molecule. B: MS/MS spectrum used to predict the sequence TCIMQLFGK. ProICAT software identified the protein as LWS opsin and these nine amino acids are an exact match to the peptide predicted from rainbow trout cDNA (AAM17921). The spectrum was validated by manual analysis. C: Ions observed in the spectra of B are highlighted in red.

C:

Residue     Mass          a           b         b-NH3         y
-------   ---------   ---------   ---------   ---------   ---------
T, Thr     101.0477     74.06      102.055      85.0284   1276.962
C, Cys    3339.1664    413.2264    441.2213    424.1948   1175.644
I, Ile     113.0841    526.3105    554.3054    537.2788    836.4777
M, Met     131.0405    657.351     685.3459    668.3193    723.3936
Q, Gln     128.0586    785.4095    813.4045    796.3779    592.3531
L, Leu     113.0841    898.4936    926.4885    909.462     464.2945
F, Phe     147.0687   1045.562    1073.557    1056.53      351.2105
G, Gly      57.0215   1102.584    1130.578    1113.552     204.1421
K, Lys     128.095    1230.678    1258.673    1241.647     147.1206