RESOLUTION OF THE ATP-DEPENDENT PROTEOLYTIC SYSTEM FROM RETICULOCYTES - COMPONENT THAT INTERACTS WITH ATP

The ATP-dependent proteolytic cell-free system from reticulocytes has been resolved into three components, each of which is absolutely required for acid solubilization of 125I-labeled bovine serum albumin radioactivity. In addition to the previously reported heat-stable polypeptide, we now describe a protein of high molecular weight (~450,000) that is labile at 42°C. The extremely heat-labile factor is remarkably stabilized by ATP. GTP and CTP, which do not stimulate proteolysis, do not stabilize this factor. Adenylate nucleotides such as ADP or the nonhydrolyzable β,Δ imido or methylene analogues of ATP cause stabilization although they do not activate proteolysis. A third protein component of the protease system, stable at 42°C, has been separated from heat-labile species by salt precipitation. All three thus far only the heat-labile factor has been shown to interact directly with ATP.