1
E013A Unique enzymes require unique analytics The existence of a different unit system for each available enzyme product on the market can be con- fusing, especially when attempt- ing to compare similar products. However, these enzyme units are not comparable, as they have mainly been devised for the pur- pose of analytical testing and quality control. As a conse- quence, the assay used to quan- tify the units for a given product is specifically designed to fit the specific enzyme involved. It may not be optimal for another enzyme of the same type. Biochemistry units defined by reaction variables In broad terms, the most frequently used definition of enzyme activity is the enzyme unit (U), defined as the amount of an enzyme that catalyzes the transformation of a specified number of substrate molecules (usually 1 micromole) per minute under certain specific reaction conditions (pH, substrate concentration, temperature and incubation time). As the reaction conditions are different for each enzyme, a multitude of different unit systems are currently used for commercial feed enzyme prod- ucts. Even though definitions can look the same for most products within a group, small details within specific assays may actu- ally differ, leading to differing outcomes and these should also be taken into account. Some examples with very different sub- strates follow: • One unit of phytase activity (FYT) is the amount of enzyme which releases 1 micromole inorganic phosphate per min from a 0.0051 M Na-phytate solution at pH 5.5 and 37 ˚C. • One unit of xylanase activity (U) is the amount of enzyme that releases 1 micromole of reducing moieties from 1.5 % arabinoxylan substrate solution per minute at pH 5.0 and 40 °C. • One protease unit (PROT) is the amount of enzyme that releases 1 micromole of p-nitroaniline from 1 millimolar substrate (Suc-Ala-Ala-Pro- Phe-pNA) per minute at pH 9.0 and 37 °C. Even for two enzymes that may have exactly the same name, for example endo-1,4-beta-xylanase – also known as EC 3.2.1.8, the definition of the units may differ as the physicochemical character- istics (e.g. pH optimum and temperature optimum) of the two enzymes could be different. How to compare similar products Even though phytase activity has been commonly determined according to the harmonized ISO 30024:2009(E) method, only four major producers have partici- pated in this process. The efficacy of a phytase will be also different for the same number of units between two products of different generations. The real value of a given enzyme product is therefore the value obtained from the animals (better performance or reduced feed costs) relative to the application dose and cost. Natu- rally, other quality parameters such as stability storage condi- tions, processing, mixability and safety also need to be taken into consideration when deciding on a product; however, basing decisions on a unit system can definitely/certainly lead to quite erroneous outcomes. Can I compare different units from different enzyme manufacturers Dr. Vibe Glitsoe Senior Department Manager Novozymes Jean-Paul Ruckebusch Global Category and Alliance Manager Feed Enzymes, DSM [email protected]
