Two-dimensional electrophoresis of proteins from cultured human retinal-pigment epithelial cells: internal references, cataloging, and glycoproteins.

Two-dimensional gel electrophoresis of acidic and basic [35S]methionine-labeled polypeptides derived from primary cultures of human retinal-pigment epithelial cells revealed about 850 proteins. By co-electrophoresis with highly purified, evolutionally conserved proteins, alpha-actinin, calmodulin, cytosol retinal-binding protein, alpha- and beta-tubulin, and vinculin (mass: 130 000 Da) were tentatively identified in the fluorograms. Quantification of greater than 100 of the excised radioactive spots by liquid scintillation counting revealed an estimated overall gel/gel and donor/donor variation of 40% (SEM, 21%), the latter for data on three to four donors 57 to 81 years old. Therefore, for a difference from normal to be significant (p less than or equal to 0.01), it would, on average, have to exceed 88% of the control mean for that protein. Putative glycoproteins were independently radiolabeled, with tritiated sugars as precursors. Glucosamine was incorporated most rapidly and with the highest specific activity. It labeled about 170 polypeptides. Fucose and N-acetylmannosamine, respectively, labeled 74 and 27 polypeptides. The glycoprotein label was maximal in about 16 very acidic proteins with apparent molecular masses between 50 000 and 150 000 Da. Parallel use of both a sugar and an amino acid label facilitates identification of proteins in two-dimensional gels.