Studies on a Mutant Form of Escherichia coli Citrate Synthase Desensitised to Allosteric Effectors

Abstract

Naturally occurring citrate synthases fall into distinct molecular and catalytic types. Gram‐negative bacteria produce a ‘large’ enzyme, allosterically inhibited by NADH and, in the facultative anaerobes such as Escherichia coli, also by 2‐oxoglutarate. On the other hand, Gram‐positive bacteria and all eukaryotes produce a ‘small’ citrate synthase which is insensitive to these metabolites. As a complement to structure‐function studies we have explored the possibility of genetically altering one type of citrate synthase to the other. By mutagenesis and suitable selection we have succeeded in isolating a mutant of E. coli whose citrate synthase is both ‘small’ and insensitive to NADH and 2‐oxoglutarate. Some characteristics of the enzyme are described. Such mutant enzymes offer a novel approach to the study of citrate synthase, its regulation and its natural diversity. Copyright © 1979, Wiley Blackwell. All rights reserved