Isolation of Kell-active protein from the red cell membrane.

Kell blood-group-active protein has been isolated by labeling red cell surface proteins with 125I, sensitizing intact cells with anti-K1, anti-K2, anti-K7, or anti-K22, solubilizing the cell membranes, isolating immune complexes, and separating their components by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Each antibody separated a protein of approximately 93,000 daltons. Periodic-acid Schiff (PAS) staining of Kell protein showed that it was glycosylated. When separated under non-reducing conditions, Kell protein had different SDS-PAGE characteristics with protein bands of approximately 85,000 daltons and 115,000 daltons. This suggests that in the red cell membrane Kell protein is complexed with other proteins. Quantitative experiments made with anti-K7, anti-K22, and a mixture of anti-K7 and anti-K22 indicate that both antigen specificities are present in the same molecule. These biochemical data support serological studies which indicate that K22 is part of the Kell system.