E013A
Unique enzymes require unique analytics
The existence of a different unit system for each available enzymeproduct on the market can be con-fusing, especially when attempt-ing to compare similar products.However, these enzyme units arenot comparable, as they havemainly been devised for the pur-pose of analytical testing andquality control. As a conse-quence, the assay used to quan-tify the units for a given productis specifically designed to fitthe 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 frequentlyused definition of enzyme activityis the enzyme unit (U), defined as the amount of an enzyme thatcatalyzes the transformation of a specified number of substratemolecules (usually 1 micromole)per minute under certain specificreaction conditions (pH, substrateconcentration, temperature andincubation time). As the reactionconditions are different for eachenzyme, a multitude of differentunit systems are currently used forcommercial feed enzyme prod-ucts. Even though definitions canlook the same for most productswithin a group, small detailswithin specific assays may actu-ally differ, leading to differing outcomes and these should alsobe taken into account. Some examples with very different sub-strates follow:
• One unit of phytase activity(FYT) is the amount of enzymewhich releases 1 micromole inorganic phosphate per minfrom a 0.0051 M Na-phytatesolution at pH 5.5 and 37 ˚C.
• One unit of xylanase activity(U) is the amount of enzymethat releases 1 micromole ofreducing moieties from 1.5%arabinoxylan substrate solution per minute at pH 5.0and 40 °C.
• One protease unit (PROT) isthe amount of enzyme that releases 1 micromole of p-nitroaniline from 1 millimolarsubstrate (Suc-Ala-Ala-Pro-Phe-pNA) per minute at pH 9.0and 37 °C.
Even for two enzymes that mayhave exactly the same name, forexample endo-1,4-beta-xylanase –also known as EC 3.2.1.8, the definition of the units may differas the physicochemical character-istics (e.g. pH optimum and temperature optimum) of the twoenzymes 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, onlyfour major producers have partici-pated in this process. The efficacy of a phytase will be also differentfor the same number of units between two products of differentgenerations. The real value of agiven enzyme product is thereforethe value obtained from the animals (better performance or reduced feed costs) relative to theapplication dose and cost. Natu-rally, other quality parameterssuch as stability storage condi-tions, processing, mixability andsafety also need to be taken intoconsideration when deciding on a product; however, basing decisions on a unit system candefinitely/certainly lead to quiteerroneous outcomes.
Can I compare different units fromdifferent enzyme manufacturers
Dr. Vibe GlitsoeSenior Department Manager
Novozymes
Jean-Paul RuckebuschGlobal Category and
Alliance Manager Feed Enzymes, DSM
E013A_Glitsoe_Ruckebusch_PA_Q8_Layout 1 03.05.13 09:13 Seite 1
