Evidence for dynamically determined conformational states in rhodanese catalysis

Area of Science:

• Biochemistry
• Enzyme kinetics
• Protein conformational dynamics

Background:

• Rhodanese enzyme exhibits hysteretic effects under specific conditions.
• Hysteresis in enzyme catalysis can arise from slow conformational changes.
• Understanding these effects is crucial for enzyme mechanism elucidation.

Purpose of the Study:

• To investigate the underlying causes of hysteretic effects in rhodanese catalysis.
• To determine the role of enzyme isomerization in observed hysteresis.
• To explore the influence of pH and ionic strength on rhodanese kinetics.

Main Methods:

• Physical and kinetic studies were employed.
• Intrinsic protein fluorescence changes were monitored.
• Enzyme interactions with thiocyanate anion were kinetically investigated.

Main Results:

• Hysteresis was observed in rhodanese catalysis at pH 5 and neutral pH with high ionic strength.
• Enzyme isomerization was implicated as the cause of hysteresis at pH 5.
• Data suggest dynamic determination of enzyme conformations during catalysis.

Conclusions:

• Enzyme isomerization is a key factor contributing to hysteresis in rhodanese.
• Catalytic cycle conformations are dynamically regulated by substrate/product concentrations.
• The interplay between conformational relaxation and catalysis influences enzyme behavior.