Role for the adenosine triphosphate-dependent proteolytic pathway in reticulocyte maturation

As reticulocytes mature into erythrocytes, organelles and many enzymes are lost. Protein degradation during reticulocyte maturation was measured by monitoring the release of tyrosine from cell proteins. Proteolysis in rabbit red blood cells was directly proportional to the number of reticulocytes and was low in erythrocytes. This process was inhibited by blockers of cellular adenosine triphosphate production and by agents, such as o-phenanthroline, N-ethylmaleimide, and hemin, which inhibit the soluble adenosine triphosphate-dependent proteolytic system. The breakdown of endogenous proteins in reticulocyte extracts was also inhibited by these agents and required adenosine triphosphate. Inhibitors of lysosomal function, however, did not affect proteolysis. Thus, the proteolytic system that degrades abnormal proteins also catalyzes the elimination of proteins during red cell development.