We also have used mass spectrometry to identify large numbers of proteins present in subcellular organelles. By first separating complex mixtures of peptides by nanoflow HPLC coupled directly to the Q-TOF mass spectrometer, we can identify many dozens of proteins at a time at low femtomolar levels, and many hundreds of proteins in a single experiment. In collaboration with Dr. Ed Ziff's group, we have identified several hundred proteins in neuronal postsynaptic densities.

Image adapted from Cover of Mol. Cell Proteomics September 2004, Vol. 3, No. 9