We have to consider that the temperature is one of the most critical conditions that rule the enzyme activity. Enzymes are proteins that solely work when they are in their proper three-dimensional conformation or shape depending on their tertiary and quaternary conformations based on the interactions of hydrogen bonds and other atomic interactions between atoms within the enzyme molecule. However, this shape is not static but is constantly expanding and contracting. This flexibility is essential to how enzymes bind to other molecules and cause chemical reactions to happen on those molecules. Lowering the temperature slows the motion of molecules and atoms, meaning this flexibility is reduced or even lost. Each enzyme has its zone of comfort (i.e., its metabolic temperature), or optimal temperature range, within which it works best. The lower the temperature the less enzyme activity and over a period of time, enzymes will be deactivated at even moderate temperatures. Storage of enzymes at 5°C or below is generally the most suitable. Some enzymes lose their activity when frozen.