• Large surfaces at the liquid–gas interface of bubbles and foams can lead to
deactivation; foaming should therefore be avoided by, e.g., addition of an
antifoam agent.
• Some agents, such as sodium azide and metal chelators (EDTA) are known to
(irreversibly) deactivate enzymes.
• When you use a solid (lyophilized or spray-dried) enzyme formulation, allow the
protein to rehydrate in the reaction buffer (at its pH optimum) for ca. 30 min
before you add the reagents.
Liquids Liquid enzyme formulations usually contain a significant amount of
stabilizing agents, such as carbohydrates, polyols and inactive (filler) proteins. In
addition, side-products from the fermentation may be present. In general, they tend
to stabilise enzymes and thus their removal (e.g., by dialysis) is not recommended.
The same applies to dilution, as concentrated protein solutions are usually more
stable. Liquid formulations should be stored in the cold (0 to +4
C), but avoid
freezing! If long-term storage is required, two options are possible (if in doubt, test
both methods on a sample first and check for any loss of activity):
• Split the liquid formulation into aliquots and shock-freeze them by dropping into
liquid nitrogen. The frozen samples can be stored at À25
C for an (almost)
unlimited period of time.
• Subject the liquid formulation to lyophilization. The latter can be conveniently
stored at 0 to +4
C.
Lyophilizates and Powders Most technical-grade enzyme preparations are
shipped as solid lyophilizates or powders. In general, they are more stable than
liquid formulations and they can be conveniently stored in the cold (0 to +4
C), but
should not be frozen! Before you open an enzyme container (from the refrigerator)
make sure that it has reached room temperature before you open it. Otherwise
moisture will condense onto the (hygroscopic) enzyme powder and will gradually
turn it into a sticky paste which goes in hand with a loss of activity. Be aware that
protein dust is more susceptible to electrostatic interaction than solid organic
compounds. Thus, enzymes tend to stick onto plastic surfaces and to spread as
dust, particularly when you collect static electricity by shuffling along a plastic lab
floor. Dissolve any solid enzymes in water before disposal.
Carrier-Fixed Immobilized Enzymes The risk of formation of dust with
immobilized enzymes is minimal. Storage at 0 to +4
C is recommended, but
avoid freezing! Any vials from the refrigerator should be brought to room temperature before opening. Due to the presence of a macroscopic carrier particle,
immobilized enzymes are particularly susceptible to mechanical disintegration.
Thus, avoid rapid stirring and agitate only by gentle shaking. Soak immobilized
enzymes in water before disposal.
5.1 Basic Rules for Handling Biocatalysts
417
deactivation; foaming should therefore be avoided by, e.g., addition of an
antifoam agent.
• Some agents, such as sodium azide and metal chelators (EDTA) are known to
(irreversibly) deactivate enzymes.
• When you use a solid (lyophilized or spray-dried) enzyme formulation, allow the
protein to rehydrate in the reaction buffer (at its pH optimum) for ca. 30 min
before you add the reagents.
Liquids Liquid enzyme formulations usually contain a significant amount of
stabilizing agents, such as carbohydrates, polyols and inactive (filler) proteins. In
addition, side-products from the fermentation may be present. In general, they tend
to stabilise enzymes and thus their removal (e.g., by dialysis) is not recommended.
The same applies to dilution, as concentrated protein solutions are usually more
stable. Liquid formulations should be stored in the cold (0 to +4
C), but avoid
freezing! If long-term storage is required, two options are possible (if in doubt, test
both methods on a sample first and check for any loss of activity):
• Split the liquid formulation into aliquots and shock-freeze them by dropping into
liquid nitrogen. The frozen samples can be stored at À25
C for an (almost)
unlimited period of time.
• Subject the liquid formulation to lyophilization. The latter can be conveniently
stored at 0 to +4
C.
Lyophilizates and Powders Most technical-grade enzyme preparations are
shipped as solid lyophilizates or powders. In general, they are more stable than
liquid formulations and they can be conveniently stored in the cold (0 to +4
C), but
should not be frozen! Before you open an enzyme container (from the refrigerator)
make sure that it has reached room temperature before you open it. Otherwise
moisture will condense onto the (hygroscopic) enzyme powder and will gradually
turn it into a sticky paste which goes in hand with a loss of activity. Be aware that
protein dust is more susceptible to electrostatic interaction than solid organic
compounds. Thus, enzymes tend to stick onto plastic surfaces and to spread as
dust, particularly when you collect static electricity by shuffling along a plastic lab
floor. Dissolve any solid enzymes in water before disposal.
Carrier-Fixed Immobilized Enzymes The risk of formation of dust with
immobilized enzymes is minimal. Storage at 0 to +4
C is recommended, but
avoid freezing! Any vials from the refrigerator should be brought to room temperature before opening. Due to the presence of a macroscopic carrier particle,
immobilized enzymes are particularly susceptible to mechanical disintegration.
Thus, avoid rapid stirring and agitate only by gentle shaking. Soak immobilized
enzymes in water before disposal.
5.1 Basic Rules for Handling Biocatalysts
417