Protein quaternary structure is the fourth classification level of protein structure. Protein quaternary structure refers to the structure of proteins which are themselves composed of two or more smaller protein chains. Protein quaternary structure describes the number and arrangement of multiple folded protein subunits in a multi-subunit complex. It includes organizations from simple dimers to large homooligomers and complexes with defined or variable numbers of subunits. In contrast to the first three levels of protein structure, not all proteins will have a quaternary structure since some proteins function as single units. Protein quaternary structure can also refer to biomolecular complexes of proteins with nucleic acids and other cofactors.
Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing in, and coughing up blood. Symptoms of a blood clot in the leg may also be present, such as a red, warm, swollen, and painful leg. Signs of a PE include low blood oxygen levels, rapid breathing, rapid heart rate, and sometimes a mild fever. Severe cases can lead to passing out, abnormally low blood pressure, obstructive shock, and sudden death.
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is formed by the action of the protease thrombin on fibrinogen, which causes it to polymerize. The polymerized fibrin, together with platelets, forms a hemostatic plug or clot over a wound site.
D-dimer is a dimer that is a fibrin degradation product, a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is so named because it contains two D fragments of the fibrin protein joined by a cross-link, hence forming a protein dimer.
Iotrolan is an iodine-containing radiocontrast agent, a substance used to improve the visibility of body structures on images obtained by X-ray techniques.
Flunixin is a nonsteroidal anti-inflammatory drug (NSAID), analgesic, and antipyretic used in horses, cattle and pigs. It is often formulated as the meglumine salt. In the United States, it is regulated by the U.S. Food and Drug Administration (FDA), and may only be lawfully distributed by order of a licensed veterinarian. There are many trade names for the product.
Diatrizoate, also known as amidotrizoate, Gastrografin, is a contrast agent used during X-ray imaging. This includes visualizing veins, the urinary system, spleen, and joints, as well as computer tomography. It is given by mouth, injection into a vein, injection into the bladder, through a nasogastric tube, or rectally.
Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions, commonly associated with direct DNA damage. Ultraviolet light induces the formation of covalent linkages between consecutive bases along the nucleotide chain in the vicinity of their carbon–carbon double bonds. The photo-coupled dimers are fluorescent. The dimerization reaction can also occur among pyrimidine bases in dsRNA —uracil or cytosine. Two common UV products are cyclobutane pyrimidine dimers (CPDs) and 6–4 photoproducts. These premutagenic lesions alter the structure of the DNA helix and cause non-canonical base pairing. Specifically, adjacent thymines or cytosines in DNA will form a cyclobutane ring when joined together and cause a distortion in the DNA. This distortion prevents replication or transcription machinery beyond the site of the dimerization. Up to 50–100 such reactions per second might occur in a skin cell during exposure to sunlight, but are usually corrected within seconds by photolyase reactivation or nucleotide excision repair. In humans, the most common form of DNA repair is nucleotide excision repair (NER). In contrast, organisms such as bacteria can counterintuitively harvest energy from the sun to fix DNA damage from pyrimidine dimers via photolyase activity. If these lesions are not fixed, polymerase machinery may misread or add in the incorrect nucleotide to the strand. If the damage to the DNA is overwhelming, mutations can arise within the genome of an organism and may lead to the production of cancer cells. Uncorrected lesions can inhibit polymerases, cause misreading during transcription or replication, or lead to arrest of replication. It causes sunburn and it triggers the production of melanin. Pyrimidine dimers are the primary cause of melanomas in humans.
Meglumine is a sugar alcohol derived from glucose that contains an amino group modification. It is often used as an excipient in pharmaceuticals and in conjunction with iodinated compounds in contrast media such as diatrizoate meglumine, iothalamate meglumine, and iodipamide meglumine.
Metrizoic acid is a pharmaceutical drug that was used as an iodinated contrast medium for X-ray imaging. Its uses included angiography and urography, but it has been discontinued, at least in the US.
Ioxitalamic acid is a pharmaceutical drug used as an iodinated contrast medium for X-ray imaging. It is used in form of its salts, ioxitalamate sodium and ioxitalamate meglumine.
Ioglicic acid is a pharmaceutical drug that was used as an iodinated contrast medium for X-ray imaging, in form of its salt meglumine ioglicate. Uses included imaging of the brain, the aorta and femoral arteries, and the urinary system.
Ioxaglic acid is pharmaceutical drug used as an iodinated contrast medium for X-ray imaging. It has low osmolality, typically resulting in fewer side effects than high-osmolality media. It is manufactured by Guerbet, but marketing in the US has been discontinued. As of 2021, it may still be available in some European countries.
Iotroxic acid, used in the form of meglumine iotroxate, is a molecule used as a contrast medium during X-rays. It is specifically used during tests looking at the gallbladder and biliary tract. It is given by slow injection into a vein.
Ioglycamic acid is a pharmaceutical drug that was used as an iodinated contrast medium for X-ray imaging of the gall bladder.
Gadoteric acid, sold under the brand name Dotarem among others, is a macrocycle-structured gadolinium-based MRI contrast agent (GBCA). It consists of the organic acid DOTA as a chelating agent, and gadolinium (Gd3+), and is used in form of the meglumine salt (gadoterate meglumine). The paramagnetic property of gadoteric acid reduces the T1 relaxation time (and to some extent the T2 and T2* relaxation times) in MRI, which is the source of its clinical utility. Because it has magnetic properties, gadoteric acid develops a magnetic moment when put under a magnetic field, which increases the signal intensity (brightness) of tissues during MRI imaging.
Delafloxacin sold under the brand name Baxdela among others, is a fluoroquinolone antibiotic used to treat acute bacterial skin and skin structure infections.
Tafamidis, sold under the brand names Vyndaqel and Vyndamax, is a medication used to delay disease progression in adults with certain forms of transthyretin amyloidosis. It can be used to treat both hereditary forms, familial amyloid cardiomyopathy and familial amyloid polyneuropathy, as well as wild-type transthyretin amyloidosis, which formerly was called senile systemic amyloidosis. It works by stabilizing the quaternary structure of the protein transthyretin. In people with transthyretin amyloidosis, transthyretin falls apart and forms clumps called (amyloid) that harm tissues including nerves and the heart.
Intravenous cholangiography is a form of cholangiography that was introduced in 1954.
Antimony potassium tartrate, also known as potassium antimonyl tartrate, potassium antimontarterate, or tartar emetic, has the formula K2Sb2(C4H2O6)2. The compound has long been known as a powerful emetic, and was used in the treatment of schistosomiasis and leishmaniasis. It is used as a resolving agent. It typically is obtained as a hydrate.
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