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Monovalent cations partially repair a conformational defect in a mutant tryptophan synthase alpha 2 beta 2 complex
S B Ruvinov1, S A Ahmed, P McPhie
1Laboratory of Biochemical Pharmacology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0830, USA.
The Journal of Biological Chemistry
|July 21, 1995
Summary
Monovalent cations like CsCl can restore activity to a mutant tryptophan synthase alpha 2 beta 2 complex. This suggests cations stabilize enzyme conformations, improving catalytic function.
Area of Science:
- Enzyme kinetics and protein biochemistry.
- Structural biology and enzyme mechanisms.
Background:
- Tryptophan synthase alpha 2 beta 2 complex activity is regulated by ligands, protein interactions, and mutations.
- The beta 2 subunit alone has low activity, enhanced by monovalent cations or alpha subunit association.
Purpose of the Study:
- Investigate how monovalent cations affect the activity and properties of a mutant alpha 2 beta 2 complex (E109A).
- Determine if cations can compensate for the loss of activity caused by the E109A mutation.
Main Methods:
- Enzyme activity assays with wild-type and E109A mutant alpha 2 beta 2 complexes.
- Spectroscopic analysis to study enzyme conformation.
- Investigated effects of various monovalent cations, including CsCl.
Main Results:
- The E109A mutant showed altered substrate specificity, active with beta-chloro-L-alanine but not L-serine.
- CsCl stimulated activity of the E109A mutant and wild-type beta 2 subunit with L-serine and indole.
- CsCl altered reaction intermediate distribution, indicating conformational stabilization.
Conclusions:
- CsCl partially rescues the E109A mutation's negative impact by stabilizing an active conformation.
- Monovalent cations stabilize enzyme conformations, influencing catalytic and spectroscopic properties, consistent with findings in other pyridoxal phosphate-dependent enzymes.