Site-directed mutagenic replacement of glu-461 with gln in beta-galactosidase (E. coli): evidence that glu-461 is important for activity.

Glutamic acid 461 of beta-galactosidase (E. coli) was replaced by gln using site-directed mutagenesis. Kinetic studies on the purified Q461-beta-galactosidase showed that it had less than 0.4% of the wild-type activity (with ONPG as substrate), confirming other studies which have suggested that the negative charge on glu-461 is important for activity. The Km values did not increase, indicating that binding of the substrate was not decreased by this change. Thermal denaturation studies showed Q461-beta-galactosidase to be somewhat more susceptible to heat denaturation than the wild-type enzyme.