Surface peptides on intact Ehrlich ascites tumor cells: Identification by a method not requiring subcellular fractionation

Abstract

Lactoperoxidase catalysed iodination of tyrosyl residues was used to label the exposed plasma membrane proteins in intact Ehrlich ascites tumor cells. Autoradiography of 125I-labeled intact cells revealed that the label was predominantly associated with the plasma membrane. When whole cells were solubilized and subjected to gel electrophoresis, two major labeled peptide classes of 100 000 and 80 000 D along with 4 minor labeled classes were found. An identical labeling pattern was obtained when plasma membranes isolated from labeled cells were solubilized and subjected to gel electrophoresis. These results demonstrate that the number of exposed plasma membrane peptides and their molecular weights can be determined without first isolating the membrane by subcellular fractionation procedures, a standard approach in most studies.