Abstract

Mutant Arg76Gln and Lys290Gln Saccharomyces cerevisiae phosphoenolpyruvate carboxykinases have been prepared and analyzed. No alteration in the apparent kinetic constants were detected for the Arg76Gln mutant enzyme, while the Lys290Gln mutant showed a 12-fold decrease in V-max/K(m)ADP. These results indicate that Arg76 is not involved in CO2 binding, but support the hypothesis that the binding of this substrate induces a conformational change that protects the region around Arg76 from trypsin action [Herrera et al. (1993) J. Protein Chem. 12, 413-418]. These findings also indicate that Lys290, a highly reactive residue against pyrydoxal phosphate [Bazaes et al. (1995), FEES Lett. 360, 207-210], does not perform an essential function for the enzyme activity.