A Comparative Analysis of the Protein Components of Plasma Membranes Isolated from Differentiated and Undifferentiated Mouse Neuroblastoma Cells in Tissue Culture

Abstract

The plasma membranes of the cells of mouse neuroblastoma clone NB41A, were isolated without fixation by hardening procedures and were characterised by their enzyme activities and by their morphology in the light and electron microscopes. The membranes were prepared from two kinds of differentiated monolayer cultures; one in which the cells were induced to form long axon‐like processes by the addition of N⁶,O^2′‐dibutyryladenosine 3′:5′‐monophosphate to the culture medium, and the other in which the cells were induced to form processes by the addition of 5‐bromo‐2′‐deoxyuridine. The proteins from the solubilised membranes were compared with similar preparations from the membranes of undifferentiated cells, grown in suspension, by sodium dodecylsulphate polyacrylamide gel electrophoresis, using the incorporation of radioactive amino acids and l‐fucose into proteins in the cultures to follow the differences in the patterns of polypeptide synthesis and glycosylation of the membrane proteins. The differentiated cells induced with either inducer show an increased incorporation of l‐fucose into two distinct components with molecular weights of 60000 and 70000. The two types of induced cells differ from each other in that N⁶,O^2′‐dibutyryladenosine 3′:5′‐monophosphate stimulates both glycosylation and protein synthesis, with a relative increase in the low molecular weight proteins, but 5‐bromo‐2′‐deoxyuridine stimulates mostly increased glycosylation of the membrane proteins.