Alteration of α‐spectrin ubiquitination due to age‐dependent changes in the erythrocyte membrane

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Abstract
Mammalian red blood cell α‐spectrin is ubiquitinated in vitro and in vivo[Corsi, D., Galluzzi, L., Crinelli, R., Magnani, M. (1995) J. Biol. Chem. 270, 8928–8935]. This process shows a cell age‐dependent decrease, with senescent red blood cells having approximately one third of the amount of ubiquitinated α‐spectrin found in young cells. In‐vitro ubiquitination of α‐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 cells catalyze the process at a reduced rate compared to those from younger cells) and on the ubiquitin isopeptidase activity (which decreases during red cell ageing). However, once α‐spectrin has been extracted from the membranes of young or old red blood cells, it is susceptible to ubiquitination to a similar extent regardless of source. This suggests that it is the membrane architecture, and not spectrin itself, that is responsible for the age‐dependent decline in ubiquitination. Furthermore, spectrin oligomers, tetramers and dimers are also equally susceptible to ubiquitination. As spectrin ubiquitination occurs on domains αIII and αV of α‐spectrin, and domain αV contains the nucleation site for the association of the α‐ and β‐spectrin chains, alterations in ubiquitination during red cell ageing could affect the stability and deformability of the erythrocyte membrane.