The katal (symbol: kat) is the unit of

catalytic activity Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

in the

International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...

(SI) used for quantifying the catalytic activity of

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s (that is, measuring the

enzymatic activity Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition. Enzyme units The quantity or concentration of an enzyme can be expressed in molar amounts, as with a ...

level in

enzyme catalysis Enzyme catalysis is the increase in the rate of a process by a biological molecule, an " enzyme". Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, cal ...

) and other catalysts. The katal is invariant of the measurement procedure, but the measured numerical value is not; the value depends on the experimental conditions. Therefore, to define the quantity of a catalyst in katals, the rate of conversion of a defined chemical reaction is specified as moles reacted per second. One katal of

trypsin Trypsin is an enzyme in the first section of the small intestine that starts the digestion of protein molecules by cutting these long chains of amino acids into smaller pieces. It is a serine protease from the PA clan superfamily, found in the d ...

, for example, is that amount of trypsin which breaks one mole of

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

bonds in one second under specified conditions.

Definition

One katal refers to an enzyme catalysing the reaction of one mole of substrate per

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ea ...

. Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice. :

\text=\frac

The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second, as

moles Moles can refer to: * Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain *The Moles (Australian band) *The Moles, alter ego of Scottish band Simon Dupree and the Big Sound People * Abraham Moles, French engin ...

per

liter The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3) ...

per second. Rather, the katal is used to express catalytic activity, which is a property of the catalyst.

SI multiples

History

The

General Conference on Weights and Measures The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...

and other international organizations recommend use of the katal. It replaces the non-SI enzyme unit of catalytic activity. The enzyme unit is still more commonly used than the katal, especially in

biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...

. The adoption of the katal has been slow.

Origin

The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978, and it became an official SI unit in 1999. The name comes from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

κατάλυσις (''katalysis''), meaning "dissolution"; the word "

catalysis Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

" itself is a Latinized form of the Greek word.

References

External links

* Unit "katal" for catalytic activity (IUPAC Technical Report) ''Pure Appl. Chem.'' Vol. 73, No. 6, pp. 927–931 (2001

* {{SI units SI derived units Units of catalytic activity Units of chemical measurement