Use of immobilized lactoperoxidase to label murine fibroblast proteins involved in adhesion to polystyrene.

Proteins involved in the attachment of murine embryo fibroblasts to polystyrene have been identified by a technique designed to iodinate only those macromolecules coming into closest apposition to the substratum. Lactoperoxidase (LPase) covalently bound to the surface of the culture flask labelled a subset of substratum-bound polypeptides with a 42,000 Mr species being most heavily labelled. Fibronectin was not labelled by this method. Soluble LPase, on the other hand, iodinated a wide range of polypeptides in cells attached to ordinary tissue culture polystyrene. Many of these polypeptides, including fibronectin, were cell-associated after scraping; however, bands of 50,000-55,000 and 42,000 Mr remained bound to the substratum. The effect of serum was investigated and the results suggested that serum components blocked labelling of the 42,000-55,000 M4 species by soluble LPase, but did not abolish labelling of similar polypeptides by the immobilized enzyme. The identity of the prominently labelled bands is discussed in the light of a functional interaction between two polypeptides, probably 10 nm filament protein subunits and actin, at sites of cell-substratum attachment.