Normal content of brain spectrin‐like protein in sph/sph mice

In the erythrocytes of WBB6F1‐sph/sph mice spectrin constitutes only ‐ 1% of the total sph/sph membrane protein compared to ‐ 23% in WBB6F1‐+/+ controls. No increase in proteolytic degradation of spectrin in sph/sph erythrocyte membranes could be detected with antibodies directed againt mouse erythrocyte spectrin or mouse brain spectrin‐like protein. As attachment of normal spectrin to the erythrocyte membrane of these animals appeared to be normal, and as spectrin not detected when whole sph/sph erythrocytes are solubilized in SDS for SDS PAGE, the deficient erythrocyte spectrin was probably due to diminished production. Brain spectrin‐like protein, a nonerythroid spectrin analogue, is antigenically, morphologically and functionally related to erythrocyte spectrin, but appears by peptide mapping analysis to be a distinct gene product. It was found by protein‐ and antibody‐staining of brain membranes to be present in normal concentrations in sph/sph animals. Indirect immunofluorescence of mouse brain tissue with anti‐brain spectrin‐like protein IgG or anti‐erythrocyte spectrin IgG indicated that the distribution of brain spectrin‐like protein was normal in sph/sph brain. Therefore the mutation causing diminished production of sph/sph erythrocyte spectrin does not affect the expression of this nonerythroid spectrin analogue.