A spectrin-like protein from mouse brain membranes: Phosphorylation of the 235,000-dalton subunit

A mouse brain spectrin-like protein, which was an immunoreactive analogue of erythrocyte spectrin, has been isolated from demyelinated membranes. This spectrin analogue was a 10.5 S, 972,000 molecular weight (M(r)) (αβ)₂ tetramer containing subunits of 240,000 (α) and 235,000 (β) M(r). We demonstrated that in vivo only the 235,000 M(r) β subunit of the mouse brain spectrin-like protein was phosphorylated, which was an analogues situation to mouse erythrocyte spectrin in which only the 220,000 M(r) β subunit was phosphorylated. Incubation of isolated membrane fractions with [γ-³²P]ATP ± adenosine 3',5'-cyclic monophosphate (cAMP) indicated that mouse brain spectrin-like protein, mouse erythrocyte spectrin, and human erythrocyte spectrin's β subunits were all phosphorylated in vitro by membrane-associated cAMP-independent protein kinases.