Thinking outside the cell: the role of extracellular adenosine triphosphate in bile formation

ATP is a highly unstable molecule. Unless quickly used to perform work, ATP spontaneously dissociates into ADP and inorganic phosphate (Pi), and the free energy released during this process is lost as heat. The energy released by ATP hydrolysis is used to perform work inside the cell and depends on a strategy called energy coupling. Cells couple the exergonic reaction of ATP hydrolysis with endergonic reactions, allowing them to proceed.
One example of energy coupling using ATP involves a...

Bile is a crucial bodily fluid, characterized by its yellow-green color and alkaline nature. Produced in the liver, it is transported through the common hepatic duct into either the cystic duct, leading to the gallbladder, or directly into the common bile duct. The flow of bile is regulated by the sphincter of Oddi located at the entrance of the duodenum. When this sphincter is closed, bile is redirected to the gallbladder for storage and concentration.
Bile is released when dietary fats enter...

The biliary system of the liver, crucial for bile secretion and drug excretion, comprises intrahepatic bile ducts that merge to form the common hepatic duct. This duct, carrying hepatic bile, combines with the cystic duct, draining the gallbladder and forming the common bile duct, which empties into the duodenum. Bile, produced by hepatic cells lining the bile canaliculi, is composed primarily of water, bile salts, pigments, electrolytes, and lesser amounts of cholesterol and fatty acids. Bile...

Adenosine triphosphate (ATP) is a critical molecule that functions as the main energy carrier in cells. Structurally, ATP consists of an adenosine molecule—comprising adenine and ribose—bonded to three phosphate groups. The high-energy bonds between these phosphate groups store significant amounts of potential energy. This energy is released during hydrolysis, wherein ATP is converted to adenosine diphosphate (ADP) or adenosine monophosphate (AMP), driving a variety of essential cellular...

The bonds of adenosine triphosphate (ATP) can be broken through the addition of water, releasing one or two phosphate groups in an exergonic process called hydrolysis. This reaction liberates the energy in the bonds for use in the cell—for instance, to synthesize proteins from amino acids.
If one phosphate group is removed, a molecule of ADP—adenosine diphosphate—remains, along with inorganic phosphate. ADP can be further hydrolyzed to AMP—adenosine monophosphate—by the removal of a second...

ATP-binding cassette or ABC transporter is the largest superfamily of integral membrane proteins. The transporters have transmembrane-binding domains (TMDs) and nucleotide-binding domains (NBDs). The TMDs are specific to their substrates, whereas the NBDs are similar to engines that complete ATP hydrolysis to complete the substrate transport. They can be full transporters consisting of two TMDs and NBDs, half transporters with one TMD and NBD, while some encoded with a single TMD or NBD are...