# E2

E2, e2, E02, E.II, e$^2$ or E-2 may refer to:

## Science and technology

* E2 reaction, a type of elimination reaction
* Honda E2, one of the predecessors of Honda's ASIMO robot
* E2, a communications channel defined in the E-carrier standard
* G$_2$ (mathematics) (old name E2 or E$_2$), a group
* E-2 process, an obsolete film developing method for photographic transparency film

### Biology and medicine

* Ubiquitin-conjugating enzyme, a protein component of proteasome-mediated protein degradation
* E2 regulatory sequence, for the insulin gene
* Levuglandin E2, an aldehyde
* Prostaglandin E2, an abortifacient
* Prostaglandin E2 receptor, a human gene
* Iodine-deficiency (ICD-10 code: E02)
* Estradiol, an estrogen steroid hormone
* Dihydrolipoyl transacetylase, the second element of the multienzyme pyruvate dehydrogenase complex
* Acireductone dioxygenase (iron(II)-requiring), an enzyme
* Haplogroup E2 (Y-DNA), a human Y-chromosome DNA haplogroup

### Computing

* E2 (cipher), a block cipher submitted to the AES competition by NTT
* Tungsten E2, a business-class Palm OS-based handheld computer
* Motorola ROKR E2, a smartphone
* Everything2, a collaborative web-based community consisting of a database of interlinked user-submitted written material

## Arts and entertainment

* E$^2$ (album), a 2007 album by Eros Ramazzotti

### Television

* "E²", an episode of Star Trek: Enterprise
* MTV e2, a Canadian entertainment news program that airs on MTV Canada
* E2 (TV channel), a Turkish TV channel
* e2 by SKY PerfecTV!, a satellite television service in Japan operated by SKY Perfect

## Transport
### Air

* Northrop Grumman E-2 Hawkeye, an American carrier-based AWACS aircraft
* Fokker E.II, a 1915 German single-seat monoplane fighter aircraft
* Pfalz E.II, a German aircraft powered by the Oberursel U.I engine
* Taylor E-2, a small, light and simple utility aircraft
* Embraer E-Jet E2 family, an updated version of the E-jet family
* Eastman E-2 Sea Rover, a 1920s seaplane
* Eurowings Europe (former IATA code: E2), an Austrian airline subsidiary of Lufthansa
* Kampuchea Airlines (former IATA code: E2), a Cambodian airline

### Rail

* E2 Series Shinkansen, a Japanese high-speed train
* EMC E2, an early American passenger-train diesel locomotive
* LB&SCR E2 class, a class of 0-6-0T steam locomotives designed by Lawson Billington
* PRR E2, an American PRR 4-4-2 locomotive
* CNW Class E-2, a class of 4-6-2 steam locomotives built by the American Locomotive Company in 1923

### Roads and footpaths

* E02 expressway (Sri Lanka), in Sri Lanka
* E2 European long distance path, a long-distance footpath that runs from Galway in Ireland to France's Mediterranean coast
* North–South Expressway Southern Route (E2), in Malaysia
* European route E002, in Azerbaijan and Armenia
* E2 expressway (Philippines), expressway route in the Philippines
* San'yō Expressway, Hiroshiwa-Iwakuni Road, Ogori Road and Yamaguchi-Ube Road, numbered as E2 in Japan

### Submarines

* HMS E2, an E-class submarine of the Royal Navy
* USS E-2, an E-class submarine of the US Navy

### Other transport

* London Buses route E2, England

## Other uses

* E-2 visa, a type of US visa
* E2, a postcode district in the E postcode area for east London, England
* Private E-2, a pay grade for the rank of Private in the US Army
* E2 (nightclub), a nightclub in Chicago, US
* Eternity II puzzle, a puzzle competition
* E-II Holdings, Inc., an investment holding company formerly owned by Meshulam Riklis, and later by Carl Icahn
* E2 grade, an assessment of difficulty in rock climbing