The inhibition of yeast enolase by Li+ and Na+1.
The activity of yeast enolase is inhibited by Li+ and Na+. At pH 7.1, inhibition by Li+ is "mixed" with respect to Mg2+; both Vmax and Km (Mg2+) are increased by Li+. The inhibition by Li+ appears to be partial, indicating that enzyme with Li+ bound is active. The step inhibited by Li+ cannot be proton abstraction since Li+ decreases the kinetic isotope effect on Vmax. At pH 9.2, where proton abstraction is no longer partially rate-limiting, inhibiton by Li+ is competitive with respect to Mg2+. The rate of enzyme-catalyzed exchange of the C-2 hydrogen with solvent is not affected by Li+. We interpret these results as follows: Li+ (and Na+) binds to enolase and decreases the rate of at least one step in the mechanism. At pH 7.1, this step is partially rate-limiting; at pH 9.2, this step is a fast step in the reaction. The step inhibited by Li+ cannot be proton abstraction but may be release of product (phosphoenol pyruvate) or Mg2+.
Kornblatt
M J
MJ
Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.
Musil
R
R
D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology*; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D010751:Phosphopyruvate Hydratase / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D012964:Sodium / Q000494:pharmacology*
D008094:Lithium; D012964:Sodium; D010751:Phosphopyruvate Hydratase; D008274:Magnesium