Enzyme activity units

The upshot of the above discussion is that a variety of enzyme activity units may be encountered. This makes it essential that all units, whatever their bases, be clearly defined. 

A third water-soluble substrate for endocellulase is hydroxyethyl-cellulose (HEC). As early as 1931, Ziese (5) used HEC and Sandegren et al. (6) defined the activity as being proportional to the change of the inverse of the specific viscosity per time unit. Child et al. (7) have also used HEC and based their calculation -on a linearization of the viscosity measurements according to Eriksson et al. (8). They defined an enzymic activity unit as the amount of enzyme causing a viscosity change of 0.001 rjre 126 min"1. The exponential factor was used in order to linearize the data. This unit is useful for comparison of cellulases of different origin, but it is based on an empirical relationship. The authors made an evaluation of their method in comparison with CMC hydrolysis. 

To obtain activity Quotients (AQ), enzyme activities (units per g liver) were divided by those in normal, adult liver. For further details see reference 5. 

Does your enzyme activity (units/mg powder) give you the same number for the different enzyme concentrations employed ... 

The reader should note that U had been reserved by chemists for the international unit of enzyme activity. However, U is often used to mean a unit of TSH concentration as defined by the WHO. To avoid confusion with enzyme activity units, lU and int units are used in this chapter to refer to the units of TSH concentration. 

There are no internationally standard assay methods for industrial enzymes and the definition of enzyme activity unit is also different for each enzyme. The activity of industrial enzymes is shown by various methods depending on manufacturers. For instance, commercial lipase activities are measured by the hydrolysis of olive oil under the various conditions and these figures are not comparable with each other. When customers apply these biocatalysts for chemical synthesis in organic solvents, these figure are sometimes reliable, and sometimes not. Users should not judge commercial enzymes based only on price and the activity shown in the table the manufacturer provides. Enzymes should be evaluated based on their practical performance under the conditions used. Most users of biotransformation are not experts in measuring enzyme activity, so the establishment of an assay method and practice are essential if one is to optimize the performance of enzymes. 

Measuring Transglutaminase Activity. Enzymic activity of transglutaminase is measured by the hydroxamate procedure with N-carbobenzoxy-L-glutaminyl-glycine (Z-Gln-Gly) (Fig. 2). The enzymic activity unit is defined as the amount causing the formation of 1 /tmole of hydroxamic acid in one minute at 37°C (7). 

Fraction Volume (ml) Protein (mg) Enzyme activity" (units 10 ) Specific activity (units 10 mg )... 

The following formula is used to calculate the apparent enzyme activity ([/, units per cm ) of the enzyme electrode ... 

Step Procedure Specific Activity (units/mg prot/30 min) Total Enzyme Activity (units/lOOg prot/30 min) Percent Recovery... 

Substrate analogues Concn. (niM) Enzyme activity (units/mg) Relative activity (%)... 

Injection Specific enzyme activity Units/mg protein S.E. ... 

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