Fig. 3.
Hybrid immunoaffinity–mass spectrometric characterization of full-length neurogranin in human brain tissue. A cluster of peaks representing full-length Ng with different sets PTMs (a). Amino acid sequence of Ng1–78 with acetyl, disulfide bridge and GSH with the positions of PTMs and b- and y-ions identified from a single MS/MS acquisition indicated (b). Full-length Ng with different PTM arrangements had different retention time during high-resolution LC–MS/MS analysis (c). Expansion of the m/z range around m/z 7500 in a MALDI mass spectrum from human brain tissue after heat-treatment without reduction with DTT showed a cluster of peaks representing Ng1–78. The rightmost peak represents Ng1–78 + acetyl + GSH + disulfide bridge (d). A similar mass spectrum from human brain tissue after heat-treatment and reduction with DTT showed another cluster of peaks representing full-length Ng. Here the peak representing Ng1–78 + acetyl + GSH + disulfide bridge was greatly reduced (e)