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Structural and functional implications of the hexokinase-nickel interaction.
1Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Journal of Inorganic Biochemistry
|November 1, 2005
Summary
Nickel binding to yeast hexokinase alters protein structure, decreasing enzyme activity. Nickel acts as a non-competitive inhibitor with glucose and a competitive inhibitor with ATP, affecting enzyme kinetics.
Area of Science:
- Biochemistry
- Enzymology
- Protein Structure
Background:
- Yeast hexokinase is a crucial enzyme in glucose metabolism.
- Understanding enzyme-ligand interactions is vital for drug development and metabolic studies.
Purpose of the Study:
- To investigate the effects of nickel ions on the structure and activity of yeast hexokinase.
- To elucidate the kinetic mechanism of nickel inhibition.
Main Methods:
- Spectroscopic techniques (e.g., circular dichroism) to analyze protein secondary structure changes.
- Enzyme kinetics assays with varying substrates (glucose and ATP) in the presence of nickel.
- Monitoring monomer/dimer equilibrium shifts.
Main Results:
- Nickel binding to yeast hexokinase exhibits positive cooperativity without reaching saturation.
- Nickel induces significant alterations in protein secondary structure, including loss of alpha-helices and beta-turns, with a gain in random coil and beta-sheet structures.
- Nickel shifts the monomer/dimer equilibrium towards the monomeric state at higher concentrations.
- Enzyme activity is reduced, with non-competitive inhibition observed when glucose is the variable substrate and linear competitive inhibition when ATP is the variable substrate.
Conclusions:
- Nickel binding induces conformational changes in yeast hexokinase, impacting its secondary structure and quaternary state.
- These structural modifications lead to a decrease in enzymatic activity.
- Nickel acts as a mixed-type inhibitor, with distinct kinetic behaviors depending on the variable substrate, highlighting its complex interaction with hexokinase.