adenosine substrate is passively transported to the cell

triphosphate binding cassete(ABC) transporter:

The human adenosine
triphosphate binding cassete (ABC) have seven subfamilies and 48 members. it is
present in all the living organisms from human to microorganisms, ABC
transporter can function as influx or efflux. ABC transporter is a membrane
protein that have the ability to bind and hydrolyze the ATP and use it as a source
of energy to efflux the substrate out of the cell, this transporter only
require energy to efflux the substance out, in the influx procedure the
substrate is passively transported to the cell with on need for energy. ABC transporters
have an important role in regulating the absorption, distribution, metabolism
and execration of cellular lipid and glucose, it controls the glucose and lipid
metabolism by regulate the secretion and activation of insulin and lipase.

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The structure
of ABC transporter:

the figure
below shows the ABC transporter structure which consist of four domains, two of
them are the binding site, it’s called trance membrane domains, the trance
membrane domains are taking place in the cell membrane, and the other two are
the ATP binding domains which are called nucleotide binding domains, they are
taking place in the cytoplasm, the trance membrane domains binds to the
substrate and the nucleotide biding domains binds to the ATP molecule.

cell cytoplasm


binding domain

membrane domain



triphosphate ride binding cassette B1 (ABCB1):

ATP binding
cassette B1 (ABCB1) transporter comes from the ATP binding cassette subfamily B
member can be classified based on the structure of the polypeptide chain
to full and half transporter, if the transporter is composed of one liked
polypeptide chain it’s called full transporter, but if the transporter is present
in tow separated polypeptide chain then it’s called half transporter. The
transporter uses the energy of ATP hydrolysis to establish a direct membrane
movement which create a pocket like structure used to transport the substrate
across the membrane. ABCB1 transporter in the abnormal condition is responsible
for giving the cancer cells it’s multidrug resisting (MDR1) property, in this case
the transporter can be named as permeability glycoprotein (p-gp). ABCB1 transporter is present in the
brush porder membrane of the intestinal cells, biliary canalicular membrane of
hepatocyte, luminal membrane of proxima, tubule epithelial cells of the kidney and
endothelial cells of blood brain barrier.


function of

the main
function of ATP binding cassette B1 (ABCB1) is to protect the cell by pumping
the toxic component or metabolite out of the cell by decreasing there exposure
to toxic molecules, as a result it limits the entry of the xenobiotic to the
cell , it works in decreasing the drug bioavailability by excreting the drug
from the body by the excretion organs like in the intestine epithelial cell
where it pumps the drug to the intestinal lumen and in the liver where it pumps
the drug to the bile duct, and protect the organs by decreasing the exposure of
the cell to the toxic xenobiotic like in blood brain barrier, testes and
placenta. This transporter Is characterized by its high transporter capacity
and its various wide substrate recognition.

When ABCB1 transporter is over excerpted it causes
multidrug resistance(MDR) which is responsible for making the resistance of
drugs in the cancer cells. permeability glycoprotein (p-gp) is a glycoprotein
encoded by the ABCB1 transporter it works in pumping the drugs to outside the cell
which makes the drug concentration inside the cell much lower than the outside,
as        a result it protects the cancer
cell from the anticancer drugs.