Effects of activators on chemically modified yeast hexokinase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Yeast hexokinase (ATP : D-hexose-6-phosphotransferase) is a crucial enzyme in glycolysis.
• Understanding the role of specific functional groups in enzyme active sites is vital for protein function studies.

Purpose of the Study:

• To investigate the role of sulfhydryl, imidazol, and amino groups in yeast hexokinase's active site and conformational changes.
• To determine how chemical modifications affect enzyme activity and response to activators.

Main Methods:

• Chemical modification of yeast hexokinase.
• Enzymatic activity assays at different pH values.
• Spectroscopic analysis (optical absorption at 286 nm).
• Enzyme denaturation studies using urea.

Main Results:

• Modification of sulfhydryl, imidazol, and amino groups did not directly implicate them in the active site.
• Chemically modified hexokinase exhibited similar transitions between inactive and active forms as the native enzyme.
• Enzyme activity and activation by citrate, D-malate, 3-phosphoglycerate, and Pi were unaffected at pH 6.6.
• Chemical modification led to an increased activation effect, suggesting active site reorganization.

Conclusions:

• Sulfhydryl, imidazol, and amino groups are not essential for yeast hexokinase's active site function or pH-dependent conformational changes.
• The observed increase in activation effect upon modification indicates a flexible active site structure that reorganizes in the presence of effectors.
• Protein structure differs significantly between pH 6.5 and 7.5, influencing denaturation rates and potentially enzyme activity.