Hormones protein-type

Ga-GDP has no affinity for the effector protein and reassociates with the p and Y subunits (A). G-proteins can undergo lateral diffusion in the membrane they are not assigned to individual receptor proteins. However, a relation exists between receptor types and G-protein types (B). Furthermore, the a-subunits of individual G-proteins are distinct in terms of their affinity for different effector proteins, as well as the kind of influence exerted on the effector protein. G -GTP of the Gs-protein stimulates adenylate cyclase, whereas G -GTP of the Gr protein is inhibitory. The G-protein-coupled receptor family includes muscarinic cholinoceptors, adrenoceptors for norepinephrine and epinephrine, receptors for dopamine, histamine, serotonin, glutamate, GABA, morphine, prostaglandins, leukotrienes, and many other mediators and hormones. 

Receptors can mediate the action of endogenous signalling compounds and may therefore be viewed as regulatory proteins. Such receptors are the physiological targets for neurotransmitters and hormones. Other types of receptors include enzyme proteins, transport proteins and structural proteins. For example, statins inhibit an enzyme catalysing the synthesis of cholesterol and loop diuretics inhibit an enzyme that facilitates the re-uptake of salt in primary urine. 

The imported proteins and receptors then go their separate ways, their fates varying with the cell and protein type. Transferrin and its receptor are eventually recycled. Some hormones, growth factors, and immune complexes, after eliciting the appropriate cellular response, are degraded along with their receptors. LDL is degraded after the associated cholesterol has been delivered to its destination, but the LDL receptor is recycled (see Fig. 21-42). 

Hormones themselves may be proteins. Notable examples are the more well-known insulin and the lesser-known thyrotropin and somatotropin (the growth hormone), as well as the ovarian luteinizing hormone and the follicle-stimulating hormone. If of relatively low molecular weight, protein-type hormones are also known as peptides, or specifically as peptide hormones. Examples listed, as a matter of course, are adrenocorticotropin, antidiuretic hormone, glucagon, and calcitonin. (Generally speaking, a peptide is a molecule with fewer than 50 amino acids, and a protein has more than 50 amino adds. The acids are combined in myriad combinations or permutations.)... 

There are two types of hormones proteins (which are also known as small peptides) and steroids. Steroids are secreted from the adrenal glands and the gonads. 

In type 1 diabetes, the treatment is obvious and effective the patients need more insulin and this can be self-delivered by injection. This only became a possibility after insulin was discovered in the 1920s by Banting and Best, and it raises new practical questions - where do we obtain the insulin and how do we process it For a long time the insulin used in medical practice was from either pig or ox pancreas. Both of these work well, but there is a problem, since the amino acid sequence of these non-human hormone proteins is not 100% identical to that of human insulin. As a result, some diabetic patients developed an immune response to the foreign... 

Two protein hormones, inhibin and activin, have been identified in gonadal tissue. Inhibin has been isolated from ovarian foUicular fluid and found to inhibit pituitary secretion of FSH. Inhibin is a glyocoprotein heterodimer consisting of two disulfide-linked subunits, a and P two types of P-subunit,... 

Several human receptors for the neurohypophyseal hormones have been cloned and the sequences elucidated. The human V2 receptor for antidiuretic hormone presumably contains 371 amino acids and seven transmembrane segments and activates cycHc AMP (76). The oxytocin receptor is a classic G-protein-coupled type of receptor with a proposed membrane topography also involving seven transmembrane components (84). A schematic representation of the oxytocin receptor stmcture within the membrane is shown in Eigure 4 (85). 

ImmunO lSS iy. Chemiluminescence compounds (eg, acridinium esters and sulfonamides, isoluminol), luciferases (eg, firefly, marine bacterial, Benilla and Varela luciferase), photoproteins (eg, aequorin, Benilld), and components of bioluminescence reactions have been tested as replacements for radioactive labels in both competitive and sandwich-type immunoassays. Acridinium ester labels are used extensively in routine clinical immunoassay analysis designed to detect a wide range of hormones, cancer markers, specific antibodies, specific proteins, and therapeutic dmgs. An acridinium ester label produces a flash of light when it reacts with an alkaline solution of hydrogen peroxide. The detection limit for the label is 0.5 amol. 

---