Testing for diffusion limitations in salt-activated enzyme catalysts operating in organic solvents.

Area of Science:

• Biochemistry
• Enzyme kinetics
• Biocatalysis

Background:

• Enzyme activity in nonaqueous media is crucial for biocatalysis.
• Lyophilization is a common method for enzyme stabilization.
• KCl has been observed to enhance enzyme activity after lyophilization.

Purpose of the Study:

• To investigate the mechanism of enzyme activation by lyophilization in the presence of KCl.
• To determine if the observed activation is due to intrinsic enzyme properties or reduced substrate diffusion limitations.
• To assess the general applicability of this phenomenon to other proteolytic enzymes.

Main Methods:

• Lyophilization of subtilisin Carlsberg with varying KCl and buffer concentrations.
• Preparation of biocatalysts with controlled ratios of active to inactive enzyme using PMSF inactivation.
• Measurement of initial catalytic rates as a function of active enzyme content.
• Comparison of activation effects in subtilisin (serine protease) and thermolysin (nonserine protease).

Main Results:

• Enzyme activation by lyophilization with KCl was independent of substrate diffusion.
• Plots of reaction rates versus percent active enzyme were linear, indicating intrinsic activation.
• Significant enzyme activation (up to 3750-fold) was observed in hexane for transesterification reactions.
• Similar activation was observed for thermolysin, suggesting a general phenomenon.

Conclusions:

• The activation of enzymes by lyophilization in the presence of KCl is an intrinsic phenomenon, not related to diffusion.
• This activation mechanism is applicable to both serine and nonserine proteases.
• Lyophilization with KCl represents a promising strategy for enhancing proteolytic enzyme activity in nonaqueous biocatalysis.