High-molecular-mass proteases (possible proteasomes) in Escherichia coli K12

Two high-molecular-mass proteases have been detected in E.coli K12 and isolated from the periplasmic fraction released by osmotic shock. The two proteases, designated Protease peri7 and Protease peri8, have similar molecular masses (greater than 2000 kDa) and degrade alpha- and beta-casein, but not insulin B chain. Protease peri7 is a metalloprotease activated 3-6 fold by ATP, dATP and GTP but inhibited by AMP. Nucleotide hydrolysis occurs during protein breakdown. Protease peri8, in contrast, is a serine protease unaffected by nucleotides or metal chelators. The two proteases appear by electron microscopy to be ring-shaped particles of approximately 125 A degrees in diameter. These proteases appear to be very similar to the multi-protease complexes (Proteasomes) detected in a variety of eukaryotic cells.