Two interconvertible forms of a purified E. coli esterase specific for APNE.

During the course of studies on proteolytic enzymes in E. coli ML 304 G [ 11, hydrolytic activity toward APNE a conventional substrate for chymotrypsin [2] was revealed in several cytoplasmic protein fractions separated on a DEAE-cellulose column. One of these esterases, with a defined R, = 0.26 in polyacrylamide gel electrophoresis, was studied in a fraction also possessing caseinolytic activity (ref. [ 11, fig. 5, band 4). The protease in this fraction was characterized and called protease C [3]. This communication describes the esterase which has been purified to homogeneity. The enzyme is not the E. coli protease I, isolated by Pacaud and Uriel [4] ; it is devoid of hydrolytic activity toward both casein and E. coli polynucleotide phosphoqlase; it appears to be an oligomeric enzyme with interesting molecular properties.