Receptor sites, on protein

Mechanistic. QSRR and those QSAR which involve enzyme reactivity can provide information about the sensitivity of a reaction to electrical effects, its electronic demand, the composition of the electrical effect and the sensitivity to steric effects. QSAR which involve binding to receptor sites on proteins can provide information about the nature of the receptor site. Other QSAR can shed light on the bioactivity-determining step. 

Neurotransmitter An organic compound capable of activating receptor sites on proteins embedded in the membrane of a neuron. 

The determination of the three-dimensional structure of molecules is a key step in the rational design of therapeutic agents that bind specifically to receptor sites on proteins and nucleic acids Case study 11.2). Consider the (hOO) planes of a crystal of an organic molecule regarded as a candidate for a drug. In an X-ray analysis the structure factors were found as follows ... 

Once the folded sequence is known, the biological and chemical properties of the protein can be predicted. In the development of drugs, for example, the intended target in the human body is a particular protein of known structure whose behavior can be altered (for the better) when a drug molecule binds to a receptor site on the target molecule. 

The first step in that process occurs when a person is exposed to HIV (usually through sexual contact or transfer of blood from an infected to a healthy person). HIV travels through the bloodstream until it comes into contact with certain types of white blood cells that contain proteins known as CD4 (cluster designation 4) receptor sites on their surface. The virus then attaches itself to the CD4 receptor and injects a protein (called the p24 protein) into the host cell s interior. The p24 protein carries the genetic information that controls reproduction of HIV. 

Any set of geometrically and energetically equivalent binding interactions between two identical polypeptide chains or proteins. In a homophilic interaction, one polypeptide chain serves as a ligand for a receptor site on the other polypeptide chain, and vice versa. 

Infection begins when specific receptor sites on the virus recognize corresponding surface proteins on the host cell. The virus penetrates the host membrane by a mechanism resembling endocytosis and is encapsulated... 

Mechanism of Action Acts as a coenzyme for various metabolic functions, including fat and carbohydrate metabolism and protein synthesis. Therapeutic Effect Necessary for cell growth and replication, hematopoiesis, and myelin synthesis. Pharmacokinetics In the presence of calcium, absorbed systemically in lower half of ileum. Initially, bound to intrinsicfactor this complex passes down intestine, binding to receptor sites on ileal mucosa. Protein binding High, Metabolized in the liver. Primarily eliminated unchanged in urine. Half-life 6 days. 

Mecftanism of Action Apiperidinethat competes with histamine for Hj-receptor sites on effector cells. Therapeutic Effect Relieves allergic rhinitis symptoms. Pfiarmacokinetics Rapidly absorbed after PO administration. Protein binding 60% 70%. Does not cross the blood-brain barrier. Minimally metabolized. Eliminated in feces and urine. Not removed by hemodialysis. Half-life 14.4 fir (increased in renal impairment). 

Mechanism of Action Aketolide that blocks protein synthesis by binding to ribosomal receptor sites on the bacterial cell wall. Therapeutic Effect Bactericidal. Pharmacokinetics Protein binding 60%-70%. More of drug is concentrated in WBCs than in plasma, and drug is eliminated more slowly fromWBCs than from plasma. Partially metabolized by the liver. Minimally excreted in feces and urine. Half-life 10 hr. 

Amino Acids and Proteins. Proteins are the molecules that perform the functions of life. They can be enzymes that catalyze biological reactions, or they can be the receptor site on a membrane that binds a specific substance. Proteins are important parts of both bones—the so-called hard biologies—and the soft biologies such as muscle and skin. Any discussion of the structure of living organisms must begin with the structure of proteins. 

Now it is probably no coincidence that in addition to occupying the benzodiazepine receptor site on the chloride ion channel protein, these remarkable drugs can also occupy the sedation-convulsant receptor of the same protein. Sedation with benzodiazepines thus goes hand in hand with anticonvulsant power—as if the two processes had some deep mediating mechanism in common with each other. What could that be ... 

A variety of signals can be transmitted across membranes without the actual flow of a substance from one side of the membrane to the other. We saw in chapter 12 that some hormones bind to specific receptor sites on the outer surface of the plasma membrane, thereby triggering metabolic changes on the cytosolic side of the membrane. Hormonal systems that function in this way are discussed in greater detail in chapter 24. Other membrane proteins mediate specific cell-cell interactions. Sometimes these interactions merely stimulate particular types of cells to bind to one another, but often they also trigger reactions that result in proliferation or differentiation of the interacting cells. We discuss signals of this type when we consider the interaction between the B and T cells of the immune system (see Supplement 3). 

Apoferritin is synthesized in response to several factors, including the presence of iron. Added iron is taken up by the iron transport protein transferrin, which then binds to receptor sites on several types of cells which store iron.1114,1115... 

The retinoids involved specifically in vision do not relate to the same chemical receptors as those found in the nutrition aspects of pharmacology. There is a different set of chemical receptors involved in the transport of retinol from the liver to the RPE cells of the retina. These receptors are found on the surface of the RPE cells and are specific for the retinoid binding proteins (RBP s) that transport the retinoids to the RPE. These RBP s play a unique role in the chromophore forming process that is not shared with the transport of retinol for purposes of metabolism and growth. Machlin says there are as many as 50,000 RBP receptor sites on the exposed surface of each RPE cell212. 

Tetracyclines inhibit bacterial protein synthesis by binding to the 30S snbnnit of the ribosome, thns blocking the attachment of aminoacyl-tRNA to the receptor site on the messenger RNA-ribosome complex. 

The cell membrane has receptor sites referred to as reactive cellular sites. Receptor sites on cell membranes are proteins, glycoproteins, proteolipids, or enzymes. 

Lectins bind to specific receptor sites on the surface of epithelial cells in the intestines which leads to a nonspecific interference with the absorption of nutrients (Liener, 1980, cited in (4)). However, the phytohemagglutinating activity can be easily eliminated by dry or thermal treatments (Liener, 1980, cited in 4)). In vitro protein digestibility of T. indica is 71.6%, which is comparable to the levels reported for Glycine max (Gross, 1982, cited in 4)). 

Theories abound, which relate those two vocabularies, but no one of them has emerged as predominant. Many of the theories suppose the existence of specific receptor sites on the surface of the receptor neurons. One hypothesis posits a set of odors of specific objects (e.g., camphor, sperm, urine, fish) that correspond to pure compounds and represent fundamental submodalities (Beets, 1982). Another (based on molecular biology) proposes dozens—perhaps hundreds—of different types of cell surface receptor proteins, each of which is tuned to a specific odorant compound or class of compounds (Buck, 1996 Zhao et al., 1998). 

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