The molecular weights of three forms of glycophorin A in sodium dodecyl sulfate solution.

The molecular weights of each of the three major forms of glycophorin A, as defined by polyacrylamide gel electrophoresis, have been determined by sedimentation equilibrium in sodium dodecyl sulfate using 2H2O to blank out the contribution of the detergent according to Reynolds and Tanford (Reynolds, J.A. and Tanford, C. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 4467--4470). The molecular weights were: form 1, 65 700; form 2, 31 100; form 4, 27 900. These data establish form 1 as a dimer, and form 2 and form 4 as monomers. 2. The relative sizes of the three forms were estimated by determining mobilities in sodium dodecyl sulfate polyacrylamide gels of gradulated gel concentrations at an ionic strength in which all three species coexist (I = 0.2). Ferguson plots show that the three species have identical net surface charge densities but differing retardation coefficients (--Kr) as follows: form 1, --0.057; 'form 4', --0.038; form 2, --0.025. From these data it is concluded that the hydrodynamic radius of form 1 is greatest, 'form 4' is intermediate, and form 2 is least.