Activation of the multicatalytic protease. The 11 S regulator and 20 S ATPase complexes contain distinct 30-kilodalton subunits.
The multicatalytic protease (MCP) associates with a 20 S ATPase complex in the presence of ATP to form the 26 S ubiquitin/ATP-dependent protease. This association results in a uniform 3-fold activation of peptide hydrolysis by MCP. In the absence of nucleotides, an 11 S regulator binds MCP and differentially stimulates its peptidase activities from 3-fold to 25-fold depending upon the peptide. When incubated separately with ATPase complex or regulator, all MCP molecules are converted to 26 S protease or to an activated MCP, respectively. Competition between ATPase complex and regulator for limiting amounts of MCP results in the 26 S protease as the only assembled species. Rabbit reticulocyte regulator is composed of a single 30-kDa protein. Among the 15 subunits in the ATPase complex, there is also a 30-kDa protein. Three findings demonstrate that the 30-kDa subunits in each complex are distinct proteins. First, two-dimensional polyacrylamide gel revealed different isoelectric points for each 30-kDa protein. Second, anti-regulator antibodies did not cross-react with proteins in the ATPase complex or in the 26 S protease. Third, directly sequenced peptides from the 30-kDa subunit of the ATPase complex are not present in the deduced amino acid sequence of the regulator. Thus, the regulator and ATPase complex are independent activators of MCP.
Hoffman
L
L
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City 84132.
Rechsteiner
M
M
D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology
D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases