Proteins from human retinal pigment epithelial cells: evidence that a major protein is actin

Two-dimensional gel electrophoresis coupled to fluorography was used to obtain the major 35S-methionine labeled protein patterns of cultured human retinal pigment epithelial cells (RPE) and fibroblasts. Comparisons of these profiles showed that: a) primary and subcultures of RPE were quite similar, each showing about 200 different proteins, b) the RPE protein patterns contained at least eight major acidic proteins (from 31 to 96 kilodaltons) not readily seen in fibroblasts; c) the fibroblast pattern showed three well-labeled, very acidic proteins, one of which (58 kilodaltons) appeared to be unique to fibroblasts; and d) a major complex of acidic protein of 43 kilodaltons with isoelectric points of 5.6 to 5.9 was a common protein in RPE and fibroblasts. These latter macromolecules were found to coelectrophorese with purified chicken muscle actin. Ultrastructural studies of cultured RPE supported the presence of actin microfilaments that were demonstrated specifically by labeling with fluorescent phallotoxin.