Catalytic-activity (cat.act.) - Dynamic NPU Manual

Catalytic-activity (cat.act.)


Enzyme activity, enzymatic activity, catalytic amount



Definition in words

Difference of amount-of-substance of component D at two points of time divided by the difference of elapsed time

Definition by equation

Note 1:Component B is catalytic component that has a property that can convert substance to a reaction product in a chemical reaction

Note 2: Component D may either be substance or reaction product

Systematic terms

Catalytic-activity of component B in system 1

Result type

Ratio scale
  • Value sets are positive numerical values
  • Algebraic operations are allowed (a=nb; a≠nb)
Numerical values from 0-∞


nkat, µkat, kat, U, kU, pU etc.

Note 1: Katal, (abbreviated “kat”), is recommended unit for catalytic-activity kind-of-quantity. (katal=mol/s)

Note 2: Enzyme unit, “U”, is acceptable for use (e.g. U, kU) but it is recommended to use katal. (U=µmol/min)

Special rule(s) in the NPU syntax

Component B is termed according to the International Enzyme Nomenclature (see Medical and metrological vocabulary).

“Procedure” is stated in the specification to the kind-of-property in the NPU definition.

“Procedure” indicates that the measurement procedure must be stated somewhere else than in the NPU code and there may be difficulties in comparing values for the same NPU code.

Non-recommended term

Amount of enzyme, amount-of-catalyst


Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p.

Laboratory field


Clinical Chemistry

Generic abbreviated Ercs(B)—Glutathione peroxidase; cat.act.(37 °C; proc.) = ? akat
Full result Erythrocytes(Blood)—Glutathione peroxidase; catalytic-activity(37 °C; procedure) = ? attokatal
Abbreviated result Ercs(B)—Glutathione peroxidase; cat.act.(37 °C; proc.) = ? akat
Written expression The catalytic-activity of Glutathione peroxidase of Erythrocytes in Mr. Smith’s blood is [?] akat. The measurement is performed at 37 °C according to a procedure defined by the laboratory
Notes Catalytic-activity is currently not in use in NPU codes. (see Details section)


NPU database, and
  • Kind-of-property

    • Nominal kind-of-property

    • Kind-of-quantity

      • Unitary kind-of-quantity

        • Rational unitary kind-of-quantity

          • Catalytic-activity


  • Dybkaer R. Concept system on ‘quantity’: formation and terminology. Accredit Qual Assur. 2013;18(3):253-60.
  • Dybkaer R. ISO terminological analysis of the VIM3 concepts ‘quantity’ and ‘kind-of-quantity’. Metrologia. 2010;47(3):127-34.
Date Term Note
2019-06-04 Catalytic-activity Term is not in use in NPU codes (see details section)
Date Notes



Catalytic-activity has not been and is currently not in use in NPU codes.

The example from the example section reflects a measurement of catalytic-activty of total glutathione peroxidase in all erythrocytes in the patient’s blood. This is currently not technical feasible. Instead, catalytic-activity may be used in combination with modifiers (e.g. concentration, content, fraction etc.), e.g. catalytic-activity concentationcatalytic-activity content etc. 


Catalytic component B is an enzyme, defined by the international enzyme nomenclature (, and shall be used for catalytic-activity kinds-of-property. Proteins are defined and termed by UNIPROT ( and should not be used in relation to catalytic-activity kinds-of-property. Though there are overlaps between these two nomenclatures..

The enzyme and protein nomenclatures can have different terms for the same molecule.

  • ABC-type protein transporter (Enzyme nomenclature, identifier EC
  • Alpha-hemolysin (Protein nomenclature, UP identifier P09616).