It is the first letter of each class. Each class in turn is subdivided into many classes, which are further divided. A four-digit enzyme commission (E.C) number is assigned to each enzyme representing class (first digit shows which of six main classes in OTHLIL), subclass (second digit), sub-sub class (third digit), and individual enzyme (fourth digit).
Class (First Digit)
It shows to which of six main classes in OTHLIL.
Subclass (Second Digit)
Oxidoreductase indicates the type of group in the donors which undergo oxidation (e.g. CH OH, aldehyde, or keto group).
Transferases indicates the nature of group which is transferred.
Hydrolases shows the type of bond hydrolysed.
Lyases shows the type of link which is broken.
Isomerase shows the type of isomerisation involved.
Ligases indicates the type of bond formed.
Sub-sub Class (Third Digit)
Oxidoreductase shows for each type of donor the type of acceptor involved (NAD and NADP).
Transferases shows the type of groups transferred.
Hydrolase shows, more precisely, the type of bond hydrolysed.
Lyase shows the nature of group removed.
Isomerase indicates, more precisely, the nature of transformation.
Ligases shows the nature of the substance formed.
Fourth digit – enzyme of its sub-sub class.
Examples:
- OxidoreductaseAlcohol dehydrogenase (alcohol NAD+ oxidoreductase E.C.1.1.1.1)
E.C.1.1.1.11 – Oxidoreductase1 – Acting on CH group of donors, which undergoes oxidation1 – with NAD+ or NADP+ as acceptor1 – Alcohol dehydrogenase - TransferasesHexokinase (ATP: D-hexose-6-phosphotranferase E.C.2.7.1.1)
E.C.2.7.1.12 – Trasferase7 – Transferring phosphate containing group1 – Phosphotransferase with a alcohol group as acceptor1 – Hexokinase - HydrolasesLipase (triacylglycerol acylhydrolase E.C 3.1.1.3)
E.C. 3.1.1.33 – Hydrolases1 – Acting an ester bonds1 – Carboxylic ester hydrolases3 – lipases - LyasesAldolase (ketose1-phosphate aldehyde lyase E.C 4.1.2.7)
E.C. 4.1.2.74 – Lyases1 – Carbon-carbon lyases2 – Aldehyde lyases7 – Aldolase - IsomerasesTriose phosphate isomerase (D-glyceraldehyde 3-phosphate ketoisomerase E.C 5.3.1.1)
E.C.5.3.1.15 – Isomerases3 – Intramolecular oxidoreductase1 – Inter-converting aldoses and ketoses1 – Triose phosphate isomerase - LigasesGlutamine synthase (α-glutamate ammonia ligase E.C 6.3.1.2)
E.C.6.3.1.26 – Ligases3 – Forming nitrogen carbon bonds1 – Acid ammonia ligases2 – Glutamine synthase
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