Asymmetric digital subscriber line

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines rather than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). Bandwidth (and bit rate) is greater toward the customer premises (known as downstream) than the reverse (known as upstream). This is why it is called asymmetric. Providers usually market ADSL as a service for consumers to receive Internet access in a relatively passive mode: able to use the higher speed direction for the download from the Internet but not needing to run servers that would require high speed in the other direction.

Overview

ADSL works by utilizing frequencies that are not used by a voice telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the telephone exchange (the last mile), typically less than 4 kilometres (2 mi), but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for further distribution.

Adenylosuccinate lyase

Adenylosuccinate lyase (or adenylosuccinase) is an enzyme that in humans is encoded by the ADSL gene.

Adenylosuccinate lyase converts adenylosuccinate to AMP and fumarate as part of the purine nucleotide cycle. ASL catalyzes two reactions in the purine biosynthetic pathway that makes AMP; ASL cleaves adenylosuccinate into AMP and fumarate, and cleaves SAICAR into AICAR and fumarate.

Adenylosuccinate lyase is part of the β-elimination superfamily of enzymes and it proceeds through an E1cb reaction mechanism. The enzyme is a homotetramer with three domains in each monomer and four active sites per homotetramer.

Point mutations in adenylosuccinate that cause lowered enzymatic activity cause clinical symptoms that mark the condition adenylosuccinate lyase deficiency.

This protein may use the morpheein model of allosteric regulation.

Function

Adenylosuccinate lyase (ASL) is an enzyme that catalyzes two reactions in the de novo purine biosynthetic pathway. In both reactions it uses an E1cb elimination reaction mechanism to cleave fumarate off of the substrate. In the first reaction, ASL converts 5-aminoimidazole- (N-succinylocarboxamide) ribotide (SAICAR) to 5-aminoimidazole-4-carboxamide ribotide (AICAR) and fumarate. AICAR proceeds through three more reactions before it becomes adenylosuccinate (also called succinyladenosine monophosphate or SAMP), which ASL then splits into adenosine monophosphate (AMP) and fumarate. ASL is important to cells not only because of its involvement in creating purines needed for cellular replication, but also because it helps regulate metabolic processes by controlling the levels of AMP and fumarate in the cell.

G.992.3

ITU G.992.3 is an ITU (International Telecommunication Union) standard, also referred to as ADSL2 or G.dmt.bis. It optionally extends the capability of basic ADSL in data rates to 12 Mbit/s downstream and, depending on Annex version, up to 3.5 Mbit/s upstream (with a mandatory capability of ADSL2 transceivers of 8 Mbit/s downstream and 800 kbit/s upstream). ADSL2 uses the same bandwidth as ADSL but achieves higher throughput via improved modulation techniques. Actual speeds may reduce depending on line quality; usually the most significant factor in line quality is the distance from the DSLAM to the customer's equipment.

Annex versions

ADSL2 has multiple modes for DSL providers to offer services for different needs. Below is a list of available features based on ADSL2 specs from the ITU standards.

See also

External links

Lex Luthor

Alexander Joseph "Lex" Luthor is a fictional supervillain appearing in American comic books published by DC Comics. Created by Jerry Siegel and Joe Shuster, Lex Luthor first appeared in Superman #4 (March 1940) and has since endured as the archenemy of Superman.

The character is a power-mad American billionaire, business magnate, gifted scientist, inventor, philanthropist to the city of Metropolis, and one of the most intelligent people in the world. A charismatic and well-known public figure, he is intent on ridding the world of alien superhero Superman, who Lex Luthor views as an obstacle to his megalomaniacal plans and as a threat to the very existence of humanity. Given Lex's high status as a supervillain, he also comes into conflict with Batman and other superheroes in the DC Universe.

Lex Luthor has traditionally lacked superpowers or a dual identity and typically appears with a bald head. He periodically wears his Warsuit, a high-tech battle suit giving him enhanced strength, flight, and advanced weaponry, among other capabilities. Lex Luthor is the owner of a corporation called LexCorp, with Mercy Graves as his personal assistant and bodyguard. Luthor has carefully crafted his public persona in order to avoid suspicion and arrest. He is well known for his philanthropy, donating vast sums of money to Metropolis over the years, funding parks, foundations, and charities.

Luthor (comics and television)

Luthor is the surname of various related fictional characters:

See also