The difference between enzyme units

May 28, 2023

Enzymes Analytics

The fact that each enzyme product on the market has its own unit system can be confusing, particularly when attempting to compare similar products. These enzyme units are not comparable since they were primarily intended for analytical testing and quality control.  As a result, the assay used to determine the number of units in a given product is customized to that specific enzyme and may be inaccurate if used for another enzyme of the same kind.

Definitions of Enzyme Units

The most commonly used definition of enzyme activity is enzyme unit (U), known as the amount of an enzyme that catalyzes the transformation of a specified number of substrate molecules (usually 1 micromole) per minute under specific reaction conditions (pH, substrate concentration, temperature, and incubation time). Since each enzyme's reaction conditions are different, many different unit systems are currently used for commercial feed enzyme products. Even though definitions for most products within an enzyme group may seem to be the same, minor details within particular assays may vary, resulting in different outcomes, and these small details should be taken into account. The following are some examples of very different substrates:

One unit of xylanase activity (U) is the amount of enzyme that releases 1 micromole of reducing sugar from a 5 mg/ml xylan solution per minute at 37℃, PH 5.5

One phytase unit (FTU) is defined as the amount of enzyme that liberates 1 micromole of inorganic phosphorus per minute from 0.0051 mol/l sodium phytate at 37℃ and pH 5.5.

One unit of alpha-amylase (U) is defined as that quantity of enzyme that will liquefy 1 g of soluble starch in 1 hour at 60 ℃ / ph 6.0.

One protease unit (U) is the amount of enzyme required as 1g solid enzyme powder produces the equivalent of 1ug tyrosine by hydrolysis per minute at 40 ℃ and pH 7.5

Even if two enzymes have the same name, for example, xylanase, the units' definition can vary due to differences in optimum pH and temperature.

Similar enzyme products comparison

The real value of a given enzyme product is the returns obtained from the animal's enhanced performance and the reduction in feed costs relative to the dose and cost.
Other quality parameters, such as stability, storage conditions, processing, mixability, and safety, should be considered when selecting a product; however, basing decisions on a unit system can undoubtedly lead to misleading results.

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