The katal (symbol: kat) is a unit of the

International System of Units The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...

(SI) used for quantifying the catalytic activity of

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s (that is, measuring the enzymatic activity level in enzyme catalysis) and other catalysts. One katal is that catalytic activity that will raise the rate of conversion by one mole per second in a specified assay system. The unit "katal" is not attached to a specified measurement procedure or assay condition, but any given catalytic activity is: the value measured depends on experimental conditions that must be specified. Therefore, to define the quantity of a catalyst in katals, the ''catalysed rate of conversion'' (the rate of conversion in presence of the catalyst minus the rate of spontaneous conversion) of a defined chemical reaction is measured in moles 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 long chains of amino acids into smaller pieces. It is a serine protease from the PA clan superfamily, found in the dig ...

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

peptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty am ...

bonds in one second under the associated specified conditions.

Definition

One katal refers to an amount of enzyme that gives a catalysed rate of conversion of one mole per

second The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...

. 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 per liter 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 (abbreviated CGPM from the ) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established in 1875 under the terms of the Metre C ...

and other international organizations recommend use of the katal. It replaces the non-SI

enzyme unit The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. 1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of one micro mole of substrate pe ...

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, a ...

. 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 classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

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

catalysis Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

" 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