The use of two dimensional electrophoresis in the characterization of the water-soluble protein fraction of commercial flat fish species

The water-soluble proteins of nine flat fish species of high commercial val ue, belonging to the Pleuronectidae, Scophtalmidae, and Soleidae families, were analyzed by two-dimensional (2D) electrophoresis, this being carried o ut by nondenaturing isoelectric focusing (IEF) in the 3.5-9.5 pH range and gradient SDS-PAGE in the 12-14% range. Most of the major proteins fell in t he 3.5-6.9 pH range. From these, the most specific proteins were in the aci dic fraction (pI<5.2; MW<16kDa). Species-specific 2D protein patterns were observed in all the nine species, and more than 25 proteins could be indivi dualized. The combination of nondenaturing IEF and gradient SDS-PAGE, both in the absence of urea, allowed detailed characterization of both the isoel ectric points and molecular weights of the major water-soluble proteins and proved to be a valuable tool for the differential characterization of the flat fish species studied.