p24 and p26, structurally related cell surface molecules identified by monoclonal antibody BA-2

This paper describes additional structural analyses of the p24 cell surface molecule recognized by monoclonal antibody BA-2. Since BA-2 is broadly reactive with a variety of normal and malignant lymphohematopoietic and nonlymphohematopoietic cells, we examined the structure of p24 expressed on different cell types. Tryptic peptide mapping and 2-dimensional gel electrophoresis of p24 isolated from colon carcinoma cells, fresh leukemic cells, leukemic cell lines, and activated T-cells indicated that p24 exhibits no structural polymorphism within the cells examined. As has recently been demonstrated with several other cell surface molecules, p24 is shown to possess a covalently-attached fatty acid, based on the incorporation of [3H]palmitate. We have also identified an additional protein, designated p26, that is coprecipitated with p24. The p26 molecule is not disulfide-linked to p24, and can be immunoprecipitated from a variety of 125I- or [35S]methionine-labeled cells. V8 protease peptide mapping indicated that p24 and p26 are structurally homologous. Pulse-chase analysis using [35S]methionine and digestion with endoglycosidase-F indicated that p24 and p26 are probably derived from a p23 precursor, but no precursor-product relationship exists between p24 and p26. Based on this data we propose that p24 and p26 are most likely differentially-processed protein products of the same gene.