The sequence of the pckA gene coding for phosphoenolpyruvate carboxykinase in Escherichia coli K-12 and previous molecular weight determinations indicate that this allosteric enzyme is a monomer of M, 51,316. The protein is homologous to ATP-dependent phosphoenolpyruvate carboxykinases from Trypanosoma brucei and Saccharomyces cerevisiwe. A potential ATP binding site was conserved in all three sequences. A potential binding site for the allosteric activator, calcium, identified in the E. coli enzyme, was only partially conserved in T. brucei and S. cerevisiae, consistent with the observation that the enzymes from the latter organisms were not activated by calcium. The published sequence of the ompR and envZ genes from Salmonella typhimurium is followed by a partial sequence that is highly homologous to pekA from E. coli. The order of these genes and the direction of transcription of the presumptive S. typhimurium pekA gene are the same as those in E. coli. The potential calcium binding site of the E. coil enzyme is conserved in the partial predicted sequence of the S. typhimurium phosphoenolpyruvate carboxykinase, consistent with the observation that calcium activation of the S. typhimurium phosphoenolpyruvase carboxykinase is very similar to that observed for the E. coli enzyme.

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