Synthesis, assembly, and turnover of alpha and beta-erythroid and nonerythroid spectrins in rat hippocampal neurons

The synthesis and turnover of alpha-erythroid, beta-erythroid, alpha-nonery throid and beta-nonerythroid spectrins was investigated in cultured rat hip pocampal neurons. [S-35]methionine and subunit specific antibodies were use d to label and immunoprecipitate newly synthesized spectrins in 12- to 14-d ay-old cultures. Synthesis experiments, performed under normal resting cond itions, showed that the ratio of newly synthesized alpha-erythroid/beta-ery throid and alpha-nonerythroid/beta-nonerythroid spectrins is 1/1 (mol/mol) both in the soluble and insoluble fractions. Soluble and insoluble alpha an d beta erythroid spectrin turn over rapidly (half-life = 16-24 min). Solubl e nonerythroid alpha-spectrin (half-life = 80 min) and beta spectrin (half- life = 53 min) turn over more slowly than their insoluble counterparts (30- 34 min). The nonerythroid alpha spectrin turnover was significantly differe nt (p < 0.05) from the other measurements except for nonerythroid beta spec trin, indicating that these subunits are protected from rapid proteolytic d egradation until they are assembled in the membrane skeleton. (C) 1999 Else vier Science. All rights reserved.