A 50 kDa, actin-binding protein in plasma membranes of rat hepatocytes and of rat liver tumors.

Plasma membranes from normal rat livers and rat liver tumors were compared by SDS-gel electrophoresis, and analyzed for actin-binding proteins by an 125I-labelled actin gel-overlay assay and by actin-affinity blotting. After treatment of rats with alpha-hexachlorocyclohexane and after induction of liver tumors by combined treatment with N-nitrosomorpholine and phenobarbital, liver plasma membranes prepared from these animals were found to be highly enriched in an actin-binding, 50 kDa polypeptide. This polypeptide seemed to be an integral protein of the plasma membrane as judged by Triton X-114-phase separation. Microsomes did not contain an actin-binding polypeptide in the 50 kDa region. Therefore, the 50 kDa protein is a candidate for interaction of actin with the liver cell plasma membrane. A possible relationship of this protein with the multi-specific, cholate transporting system of the rat liver plasma membrane is discussed.