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A new ATP-dependent, casein-degrading proteolytic complex has been identified and partially purified from Escherichia coli. The proteolytic complex can be isolated from wild-type cells as well as from mutants in which the gene for the ATP-dependent Lon protease is deleted. The complex consists of at least two components (components I and II) that can be separated from each other (and from wild-type Lon protease) by phosphocellulose chromatography. Neither component has casein-degrading activity when added separately to assay solutions with or without ATP. Both components must be present simultaneously for casein degradation to occur. Of the nucleotides tested, only ATP activates the proteolytic complex, and the ATP must be present continuously for degradation to occur. Component II copurifies with an ATPase activity and binds to a Type 4 ATP affinity column. ATP protects component II from heat inactivation, suggesting that component II interacts with ATP. Proteolysis was not inhibited by any serine protease inhibitors but was inhibited by reagents such as the organomercurial Neohydrin and N-ethylmaleimide, which react with sulfhydryl groups. Our data provide convincing evidence that E. coli possesses a previously undescribed proteolytic system composed of at least two complementary components and absolutely dependent on ATP.
Katayama-Fujimura et al. (Wed,) studied this question.