Heterogeneity of a tumor surface protein (designated TSP-180) has been demonstrated by two-dimensional electrophoresis. Line 1 carcinoma cells derived from a spontaneous alveolar carcinoma of BALB/c mice were labeled externally with 125I by use of lactoperoxidase or metabolically with [3H]-leucine before cell proteins were solubilized with Triton X-100 detergent. Immunoprecipitates prepared with heterologous antisera allowed comparison of two-dimensional patterns of line 1 surface proteins labeled with 125I or 3H. The isoelectric point of 125I-labeled TSP-180 was heterogeneous and varied between 6.1 and 6.3. Treatment with neuraminidase shifted the pl values to between 5.9 and 6.1 and reduced, but did not eliminate, the banding heterogeneity. These data show that charge heterogeneity due to sialization, as well as other factors, exists in TSP-180.

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Research sponsored by NIH Grant CA 24553-01 and the Office of Health and Environmental Research, United States Department of Energy, under Contract W-7405-eng-26 with the Union Carbide Corporation. This is Paper 3 of a series of papers on this subject.

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