Alteration of alpha-spectrin ubiquitination due to age-dependent changes in the erythrocyte membrane

Mammalian red blood cell a-spectrin is ubiquitinated in vitro and in vivo [ Corsi, D., Galluzzi, L., Crinelli, R., Magnani, M. (1995) J. Biol. Chem. 27 0, 8928-8935]. This process shows a cell age-dependent decrease, with senes cent red blood cells having approximately one third of the amount of ubiqui tinated alpha-spectrin found in young cells. In-vitro ubiquitination of ol- spectrin was dependent on the source of the red cell membranes (those from older cells are less susceptible to ubiquitination than those from younger cells), on the source of ubiquitin-conjugating enzymes (those from older ce lls catalyze the process at a reduced rate compared to those from younger c ells) and on the ubiquitin isopeptidase activity (which decreases during re d cell ageing). However, once ol-spectrin has been extracted from the membr anes of young or old red blood cells, it is susceptible to ubiquitination t o a similar extent regardless of source. This suggests that it is the membr ane architecture, and not spectrin itself, that is responsible for the age- dependent decline in ubiquitination. Furthermore, spectrin oligomers, tetra mers and dimers are also equally susceptible to ubiquitination. As spectrin ubiquitination occurs on domains (alpha III and alpha V of alpha-spectrin, and domain aV contains the nucleation site for the association of the alph a- and beta-spectrin chains, alterations in ubiquitination during red cell ageing could affect the stability and deformability of the erythrocyte memb rane.