Nonstereospecific substrate usage by glyoxalase I.

Area of Science:

• Biochemistry
• Enzymology

Background:

• Glyoxalase I enzyme acts on thiohemiacetals formed from glutathione and alpha-ketoaldehydes.
• These substrates exist as rapidly interconverting diastereomers.

Purpose of the Study:

• To investigate substrate utilization by glyoxalase I from yeast and porcine erythrocytes.
• To elucidate the catalytic mechanism of glyoxalase I.

Main Methods:

• Isotope-trapping experiments using [3H]glutathione and phenylglyoxal.
• Varying concentrations of glyoxalase I in chase solutions.
• Analysis of competitive inhibition by para-substituted S-(phenylethenyl)glutathione derivatives.

Main Results:

• Demonstrated that glyoxalase I utilizes both diastereomeric thiohemiacetals as substrates.
• Observed near 100% incorporation of radioactivity into the product at high enzyme concentrations.
• Identified cis and trans isomers as strong competitive inhibitors.

Conclusions:

• Glyoxalase I accommodates both diastereomeric substrate forms within its active site.
• A catalytic mechanism involving interconversion of bound diastereomers is proposed.
• Enzyme properties explain substrate and inhibitor interactions.