Identification and purification of a Mr 75,000 cell surface human melanoma-associated antigen

Surface macromolecules on cultured human melanoma cells wee radioiodinated by a lactoperoxidase method. Macromolecules shed into culture medium were collected, concentrated, and fractionated on Sepharose 6B and lentil lectin-Sepharose. Radioactivity associated with macromolecules was assayed by precipitation with trichloracetic acid, and that associated with melanoma-associated antigens (MAA) was assayed by specific immunoprecipitation with xenogeneic anti-melanoma serum. Following the last step in purification, approximately two-thirds of the acid-insoluble radioactivity in the most MAA-active fraction was associated with this antigen. MAA concentration in this fraction was approximately 200-fold greater than that in cells, and it contained a single labeled protein band by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The MAA was a glycoprotein consisting of a single polypeptide chain with a molecular weight of approximately 75,000. This antigen was common to several but not to all melanomas. It was not detected, or was present in much decreased concentration, in 16 other unrelated allogeneic or xenogeneic normal and malignant cells. It was immunologically unrelated to serum albumin or fibronectin. These observations indicate that we have highly purified a Mr 75,000 cell surface component of human melanoma cell which appears to be a MAA.