Erythrocyte membrane skeletal protein bands 4.1 a and b are sequence-related phosphoproteins.

Bands 4.1 a and b are proteins of 80,000 and 78,000 molecular weight, which are both present at approximately 100,000 copies per erythrocyte ghost. Both proteins are components of the erythrocyte membrane skeleton. Bands 4.1 a and b are labeled when intact erythrocytes are incubated with [32P]orthophosphoric acid, and, therefore, are phosphoproteins. One-dimensional partial proteolytic mapping analysis of 32P-labeled bands 4.1 a and 4.1 b and two-dimensional peptide mapping analysis of 125I-labeled bands 4.1 a and 4.1 b clearly demonstrated that the two proteins are sequence-related phosphoproteins. Band 4.1 purified by standard techniques (Tyler, J. M., Hargreaves, W. R., and Branton, D. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 5192-5196) contains bands 4.1 a and 4.1 b. Bands 4.1 a and 4.1 b bind to spectrin heterodimers in solution. We conclude that the erythrocyte skeletal proteins bands 4.1 a and 4.1 b are sequence-related phosphoproteins, both capable of binding spectrin.