10.542 /10.442 Biochemical Engineering

Spring 2005

En zym e Nomencla ture

Enzym e s are class i fied into six different gr oup s accord ing to the reaction being cataly zed. The nom enc l ature was determ ined by the En zyme Comm ission in 1961 (with the latest update having occurred in 1992), hence all en zym e s are assigned an “EC” num ber. The classification does not take into account am ino acid sequence (ie, hom ology), protein structure, o r chem ical m e chanism .

EC num b ers are four dig its, for exam ple a.b.c.d, where “a” is the class, “b ” is th e subclass, “c” is the sub-subcla ss, an d “d” is the sub-sub-sub class. The “b” and “c” d i gits describe the reaction, while the “d” digit is used to distingu ish between different enzym e s of the sam e function based on the actual substrate in the reaction.

Th e Si x Classes

EC 1. Oxidoreductases – catalyze the transfer of hydrogen or oxygen atom s or electrons from one substrate to another, also called oxidases , dehydrogenases, or reductases . Note that sin ce these are ‘redox’ re actions, an electron donor/accepto r is also required to com p lete the reaction.

EC 2. Transferases – catalyze group transfer re actions, excluding oxidoreductases (which transfer hydrogen or oxygen and are EC 1). These are of the general form :

A-X + B ↔ BX + A

EC 3. Hydrolases – catalyze hydrolytic reactions. Includes lipases, esterases, nitrilases, peptidases/proteases . Th ese are of the general form :

A-X + H 2 O ↔ X-OH + HA

EC 4. Lyas es – catalyze non-hydrolytic (covered in EC 3) rem oval of functional groups from substrates, often creati ng a double bond in the product; or the reverse reaction, ie, addition of function groups across a double bond. Includes d e carboxylas es and aldolases in the rem o val direction, and synthases in the addition direction.

EC 5. Isomerases – catalyzes isomerization reactions , including racem i zations and cis- tran isom erization s.

EC 6. Ligases -- catalyzes the synthesis of various (m ostly C-X) bonds, coupled with the breakdown of energy-containing substrates, usu . ATP

The various sub n -classes are defined based on the prim ar y class. A list of the subclasses for each clas s is given b e low. Additional in formation on the sub-subclass es and sub-s ub- subclasses (ie, full enzym e classification a nd nam e s) can be found at the referenced web link.

Fro m th e We b version , http://www.ch em.qmul.ac.uk/iubmb/enzyme/index.html

Enz y me Subclasses

The links are to a list of sub-subclasses which in turn list the enzym e s linked to sepa r a te files for each enzym e , or to a list as part of a f ile with up to 50 enzym e s per file.

Content rem oved due to copyright restricti ons. P l ease see "E nzym e Subc lasses" table on http://www.chem .q mul.ac.uk/iubm b/enzym e /index.htm l

Enzym e Nom e nclature p. 2