Ubiquitin-mediated processes in erythroid cell maturation.

Response of the ATP, ubiquitin-dependent system during the enhanced degradation of erythrocyte maturation conforms to the general regulatory features common to several similar but unrelated systems. In erythroid cells enhanced degradation follows three phases: (1) Onset of degradation characterized by an increase in the intracellular concentration of free and conjugated ubiquitin, brought about by reduction in mean cell volume; (2) Active enhanced degradation during cellular remodeling; and (3) Loss of activity as a consequence of spontaneous inactivation of components required for ubiquitin conjugation. The extent of degradative remodeling is probably functionally limited by the loss of these critical ligation enzymes.