Isolation and characterization of a serologically defined tumour membrane antigen from a chemically-induced rat...

Polypeptides containing the tumour antigenic determinant present on the external domain of a membrane antigen of the 3-4 benzpyrene-induced rat fibrosarcoma HSN have been isolated and purified. Following cleavage from intact cells with trypsin, the peptides were purified by immunoaffinity chromatography and SDS-PAGE. Three polypeptides of molecular weight 120, 45 and 42 kDa were obtained that bound the specific rat monoclonal antibody (MAb) 11/160 in Western blots. Chemical analyses of the 45-kDa fragment yielded the following sequence: NH2-I V F P H G S L M V I L E H T Q K P All 14 of the syngeneic MAbs prepared from rats bearing the HSN tumour competed with each other to bind to the specific antigen. Western blots of the purified tryptic fragments probed with 125I-AbI revealed that, while some of the MAbs (11/160, ALN/12/17 and ALN/9/94) recognized a sequential determinant, others (ALN/11/53, ALN/16/53, and AL/3/12) bound to a conformational epitope. It is concluded that the AbI bind to distinct but overlapping epitopes.