Other Patterns of Regulation of the Synthesis of Amino Acids of the Aspartate Family

Abstract

It appears that all Enterobacteriaceae make use of the three isofunctional enzymes to accomplish a differential control of the aspartokinase activity. The inhibition and repression patterns found in Escherichia coli and Salmonella typhimurium are also found in other coliform bacteria such as Edwardsiella tarda, Aerobacter aerogenes and A. cloacae, Serratia marcescens, Erwinia carotovora and E. aroideae, Proteus vulgaris and Providencia sp. The relative activity of the three aspartokinases (measured in crude extracts) differ greatly from strain to strain, even within a single species and probably reflect a different degree of repression due to the different size of the individual free amino acids in the cytoplasm. Like E. coli and S. typhimurium, all strains examined contain a homoserine dehydrogenase partly inhibitable by threonine. The possible physical association between aspartokinase I and II with homoserine dehydrogenase in the other coliforms has not been examined, since this is a property determinable only after some degree of enzyme purification.