Although many abundant proteins of the postsynaptic density (PSD) are known, most of the less abundant and minor PSD proteins await identification. In this work we attempted to identify a 37 kDa protein, which represented less than 1% of the total n-o...
Although many abundant proteins of the postsynaptic density (PSD) are known, most of the less abundant and minor PSD proteins await identification. In this work we attempted to identify a 37 kDa protein, which represented less than 1% of the total n-octyl glucoside (NOG)-insoluble proteins, by protein sequencing. To enrich the target protein, the NOG-insoluble fraction was first electrophoresed in 6% SDS-polyacrylamide gels, and the proteins smaller than 45 kDa compressed in the gel front were electroeluted and subsequently reseparated in 10% SDS-gels. This procedure enriched the target protein to represent about 25% of the eluted proteins. Peptides were generated by digesting the target protein with trypsin directly in the gel and purified by a reverse phase high performance liquid chromatography (HPLC). Two peptides were determined for amino acid sequences. A database search revealed that both sequences were found in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) with a minor discrepancy, indicating that the 37 kDa protein in the NOG-insoluble PSD fraction is an isoform of GAPDH.