Active site

In biology, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of residues that form temporary bonds with the substrate (binding site) and residues that catalyse a reaction of that substrate (catalytic site). The active site is usually a groove or pocket of the enzyme which can be located in a deep tunnel within the enzyme, or between the interfaces of multimeric enzymes. An active site can catalyse a reaction repeatedly as its residues are not altered at the end of the reaction (they may change during the reaction, but are regenerated by the end).

Binding site

Usually, an enzyme molecule has only one active site, and the active site fits with one specific type of substrate. An active site contains a binding site that binds the substrate and orients it for catalysis. Residues in the binding site form hydrogen bonds, hydrophobic interactions, or temporary covalent interactions (van der Waals) with the substrate to make an enzyme-substrate complex. In order to function, the active site needs to be in a specific conformation and so denaturation of the protein by high temperatures or extreme pH values will destroy its catalytic activity. A tighter fit between an active site and the substrate molecule is believed to increase efficiency of a reaction. Most enzymes have deeply buried active sites, which can be accessed by a substrate via access channels.

Active

Active may refer to:

Music

Ships

Computers and electronics

Bioavailability

In pharmacology, bioavailability (BA) is a subcategory of absorption and is the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered intravenously, its bioavailability is 100%. However, when a medication is administered via other routes (such as orally), its bioavailability generally decreases (due to incomplete absorption and first-pass metabolism) or may vary from patient to patient. Bioavailability is one of the essential tools in pharmacokinetics, as bioavailability must be considered when calculating dosages for non-intravenous routes of administration.

For dietary supplements, herbs and other nutrients in which the route of administration is nearly always oral, bioavailability generally designates simply the quantity or fraction of the ingested dose that is absorbed.

Bioavailability is defined slightly differently for drugs as opposed to dietary supplements primarily due to the method of administration and Food and Drug Administration regulations.

Active (1877)

The Active was a wooden ketch that was wrecked on the Oyster bank at the entrance of Newcastle Harbour, New South Wales, near the previously wrecked Colonist on 19 January 1898 while carrying a cargo of ironbark to Morpeth, New South Wales under the command of Captain P. Williams. There were no casualties but the ship was lost. The wreck has not been located, but the approximate co-ordinates of the shipwreck are 32°55′S 151°47′E / 32.92°S 151.79°E / -32.92; 151.79Coordinates: 32°55′S 151°47′E / 32.92°S 151.79°E / -32.92; 151.79.

References

Further reading

Online databases
Australian National Shipwreck Database
Australian Shipping - Arrivals and Departures 1788-1968 including shipwrecks
Encyclopaedia of Australian Shipwrecks - New South Wales Shipwrecks

Books