Determination and characteristics of energy-dependent proteolysis in rabbit reticulocytes.

1. A method is reported, based on the isotopic dilution of lysine, which is suitable for the measurement of the degradation of stroma proteins of reticulocytes. 2. Proteolysis is extensive and time-limited. It may reach 50% of the stroma in 2 h at pH 7.6 and 37 degrees C. It is strongly dependent on pH and temperature, being small at low pH and temperatures. Proteolysis is largely ATP-dependent. The extent of proteolysis is nearly proportional to the degree of reticulocytosis. 3. The proteolytic system may be reconstructed in hemolysates if ATP is produced or supplied. It is assumed that the system is identical and that studied by Goldberg et al. and Hershko et al. on abnormal or denatured proteins as substrates. The main significance of the proteolytic system appears to be the degradation of mitochondria during maturation of the red cell.