Magnesium ion requirements for yeast enolase activity

Area of Science:

• Biochemistry
• Enzymology
• Protein-metal interactions

Background:

• Enolase is a crucial enzyme in glycolysis, catalyzing the interconversion of 2-phosphoglycerate and phosphoenolpyruvate.
• Previous studies suggested that only two divalent cations are necessary for enolase activity.
• Enolase is known to bind four metal ions in the presence of substrate, creating a discrepancy in understanding its activation stoichiometry.

Purpose of the Study:

• To re-evaluate the stoichiometry of metal ion activation for the enzyme enolase.
• To determine the precise number of magnesium ions (Mg2+) required for optimal enolase enzymatic activity.
• To elucidate the mechanism of enolase activation and inhibition by Mg2+.

Main Methods:

• Specific ion electrode measurements were used to quantify Mg2+ binding to enolase in the presence and absence of substrate.
• Stopped-flow spectrophotometry was employed to measure the reaction velocity of 2-phosphoglycerate dehydration.
• Kinetic analysis was performed to correlate Mg2+ binding with enzyme activity.

Main Results:

• Enolase exhibits no activity when only two Mg2+ binding sites are occupied.
• Full enzymatic activity is achieved only when all four Mg2+ binding sites are populated.
• An ordered binding mechanism for Mg2+ was proposed, accurately predicting enolase activation.
• Excessive Mg2+ concentrations lead to a loss of enzymatic activity, indicating inhibition.

Conclusions:

• Four Mg2+ ions are essential for the full catalytic activity of enolase.
• A model involving ordered binding of four Mg2+ ions quantitatively explains enolase activation.
• The binding of additional Mg2+ ions at higher concentrations results in enzyme inhibition.