Enzyme unit
The enzyme unit ( U ) is a unit of enzyme activity that has been replaced by the katal (in Germany, the katal has been the legal unit in metrology since October 3, 2009). Since the numerical values change when using the katal, the enzyme unit is still used in medicine and clinical chemistry .
One unit of enzyme corresponds to a micro- mol substrate turnover per minute under defined conditions:
The conditions (temperature, substrate concentration, pH value, etc.) should be chosen so that a maximum reaction rate is achieved. This makes corresponding additional information necessary and makes it difficult to compare information. A uniform temperature of at least 30 ° C is therefore often used as a basis.
Since catalytic activity and enzyme amount are directly related to the turnover number of the enzyme, information in U is often used as a measure of the enzyme amount. For example, commercially available enzymes for molecular genetics are often sold staggered according to enzyme units. For restriction endonucleases , however, these are usually defined by the complete digestion of 1 μg of genomic DNA of the λ phage in one hour under certain reaction conditions; if λ-DNA is not cut, the definition is based on another DNA, e.g. B. the adenovirus 2 genome.
literature
- ↑ Third ordinance amending the Units Ordinance of September 25, 2009 ( Federal Law Gazette I p. 3169 ).
- ↑ International Union of Biochemistry: Report on the Commission on Enzymes of the International Union of Biochemistry , Pergamon Press, New York, 1961, p. 8.