[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Enzyme units, specificity and uses in medicine and industry

# Enzyme units, specificity and uses in medicine and industry

How enzyme activity is counted, how picky enzymes are, and how they are engineered, fixed to surfaces or given as drugs.

Updated Nov 12, 2026

## Key facts

- International unit (U): the amount of enzyme that converts 1 µmol of substrate per minute under stated conditions; serum enzymes are reported in U/L.
- Katal (kat): the SI unit, 1 mol of substrate per second; 1 U is about 16.67 nkat.
- Specific activity (units per mg of protein) rises as an enzyme is purified; the turnover number (kcat) counts reactions per enzyme molecule per second.
- Specificity can be absolute (urease acts only on urea), for a group or bond (trypsin cuts after lysine or arginine) or for one stereoisomer (most human enzymes use L-amino acids and D-sugars).
- Enzymes are named and numbered (EC numbers) by the IUBMB in six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases (a seventh, translocases, was added in 2018).

## In detail

- Measured activity depends on temperature, pH and substrate concentration, so results are comparable only within one laboratory method.
- Enzyme engineering changes amino acids, by site-directed mutagenesis or directed evolution, to make an enzyme more stable, faster or able to use a new substrate.
- Immobilised enzymes are fixed to a solid support so they can be reused or run continuously: glucose isomerase for high-fructose syrup, glucose oxidase on test strips and glucose sensors.
- Enzymes used for diagnosis measure analytes specifically: glucose oxidase or hexokinase for glucose, uricase for uric acid, cholesterol oxidase for cholesterol.

**Also called**
International unit and katal, Immobilised enzymes

## Clinical notes

- Enzymes as drugs: thrombolytics (alteplase, streptokinase), asparaginase in acute lymphoblastic leukaemia, dornase alfa in cystic fibrosis, pancreatic enzymes for malabsorption and enzyme replacement in lysosomal storage diseases (Gaucher disease).
- Glucose meters and urine strips work because glucose oxidase is specific for glucose.

## Test yourself

Think of the answer, then tap the question to see it.

## What is one international unit of enzyme activity?

The amount of enzyme that converts 1 µmol of substrate per minute under stated conditions.

## Why is a serum enzyme result from one laboratory not always comparable with another?

Activity depends on the method's temperature, pH and substrate, which differ between laboratories.

## What is the advantage of immobilising an enzyme?

It can be reused or run continuously and separated easily from the product, as on glucose test strips and sensors.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/enzyme-units-specificity-and-uses-in-medicine-and-industry/)

## Connections

## Related conditions 2

- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Gaucher disease](https://durgical.com/en/conditions/gaucher-disease/)

## Related 4

- [Enzyme kinetics (Michaelis–Menten and Lineweaver–Burk)](https://durgical.com/en/biochemistry/topics/enzyme-kinetics/)
- [Isoenzymes](https://durgical.com/en/biochemistry/topics/isoenzymes/)
- [Types of enzyme inhibition](https://durgical.com/en/biochemistry/topics/types-of-enzyme-inhibition/)
- [Recombinant DNA and cloning](https://durgical.com/en/biochemistry/topics/recombinant-dna-and-cloning/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Enzyme Nomenclature](https://iubmb.qmul.ac.uk/enzyme/) (International Union of Biochemistry and Molecular Biology (IUBMB), 2026).

[← All of biochemistry](https://durgical.com/en/biochemistry/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/biochemistry/topics/enzyme-units-specificity-and-uses-in-medicine-and-industry/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/enzyme-units-specificity-and-uses-in-medicine-and-industry/