Trigger reaction

Fig. 4.1.15 Comparison of the luminescence and fluorescence emission spectra of natural aequorin (left panel) and recombinant e-aequorin (right panel) the luminescence spectra of Ca2+ -triggered reaction (dark solid lines), the fluorescence emission spectra of the spent solution containing 2 mM Ca2+ (dashed lines), and the luminescence spectra of the spent solution after addition of coelenterazine (light solid lines). Reproduced with permission, from Shimomura, 1995d. the Biochemical Society.

The epidermal growth factor receptor 2 (HER-2) is a protein found on the surface of cells. Heterodimerization of HER-2 activates the enzyme tyrosine kinase, triggering reactions that cause the cells to grow and multiply. HER-2 is found at abnormally high levels on the surface of many types of cancer cells, which may divide excessively. Antibodies targeting HER-2 (e.g., trastuzumab) are used as antineoplastic agents. 

Tertiary amines also depolymerize lithium alkyl tetramers and hexamers and can be used to trigger reactions with alkyl halides (Lepley, 1968). However, when triethylamine is used to initiate the butyl... 

The chemistry involved in this explosively unstable system is reviewed [1]. The mechanism of the trigger reactions that initiate the exothermic decomposition of chlorate-sulfur mixtures has been studied. Mixtures containing 1-30% of sulfur can decompose well below the m.p. of sulfur, and addition of sulfur dioxide, the suspected chemical trigger, causes immediate onset of the reaction [2], Autoignition of stoichiometric mixtures can be as low as 115°C, with frictional sensitivity at 5N, the lowest load the test apparatus permitted. Both were dependent upon the history of the sulphur used [3],... 

Anion-triggered reactions, as discussed earlier in Chapter 2, embody transformations in most cases, in which a nucleophile acts as the attacking species towards an electrophile. Since oxidation and reduction procedures are well established for providing nucleophilic or electrophilic functionalities, they can be combined with anionic process. 

Enzymatic trigger reaction Effect of trigger reaction Domino process... 

In another approach, the alcohol moiety, formed by an enzymatic hydrolysis of an ester, can act as a nucleophile. In their synthesis of pityol (8-37a), a pheromone of the elm bark beetle, Faber and coworkers [17] used an enzyme-triggered reaction of the diastereomeric mixture of ( )-epoxy ester 8-35 employing an immobilized enzyme preparation (Novo SP 409) or whole lyophilized cells of Rhodococcus erythro-polis NCIMB 11540 (Scheme 8.9). As an intermediate, the enantiopure alcohol 8-36 is formed via kinetic resolution as a mixture ofdiastereomers, which leads to the diastereomeric THF derivatives pityol (8-37a) and 8-37b as a separable mixture with a... 

Magnesium, Mg2+ 6, octahedral O-Carboxylate, phosphate Structure in hydrolases, isomerases, phosphate transfer, trigger reactions... 

A loss in viscosity occurs when enzymes, organic catalysts manufactured by bacteria and/or fungi, start to destroy the thickener. These enzymes are capable of triggering reactions quickly and for indefinite periods. One enzyme molecule can effectively change millions of raw material molecules to undesirable end products. The result can be a paint or coating that loses its elastic and elonga-tional properties. 

Mechanical destruction of cells, as it occurs as a result of a trauma, is the most unspecific way of histamine release. Another important mechanism are allergic reactions. The triggering reaction is the binding of an antigen at immunoglobulin E (IgE) antibodies present at the surface of mast cells. A series of reactions, one of which is a calcium influx, leads... 

Synaptic cleft Gap of about 100 300 pm in diameter between two neurons. A neurotransmitter is released from the first neuron into the synaptic cleft and may interact with a receptor located on the membrane of the second neuron to trigger reactions leading to the propagation of information... 

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). 

The two hormones that we have just discussed are part of a larger picture, which includes many hormones that directly affect most tissues in the vertebrate. Each hormone is synthesized in a specialized endocrine gland (fig. 24.6 and table 24.3) and is secreted under special circumstances. Once secreted, the hormone diffuses throughout the entire organism, but it triggers reactions only in those cells that carry specific receptors for the hormone. 

An example is calicheamicin, which is able to form the reactive diradical species even under physiological conditions. Here, the Bergman Cyclization is activated by a triggering reaction. A distinguishing property of this diradical species is that it can effect a dual-strand cleavage of DNA ... 

Of great interest is the creation of trigger reaction ensembles, which will not only change the interference picture but also the type of interacting reaction with respect to the action of temperature, pressure, medium pH and other important factors. 

At a specified point in the tank, 100 cm of hydrochloric acid 1.2N(Cg0 = 0.83 moles. m- after complete mixing in the tank in the absence of reaction) were injected by means of a cylinder obturated at its lower end by an elastic membrane which becomes inflated and bursts out when submitted to the pressure of the liquid pushed by a piston. The acid was thus injected without any preferential direction. This locally released acid B triggers reactions f2j and 3]. If the local micromixing state is perfect, the acid is totally and instantaneously neutralized, as it is in stoichiometric defect with respect to A. The first reaction being very fast as compared to the second one, the precipitate S does not appear. Conversely, if mixing of the acid is not instantaneously... 

The light-driven, energy- and electron-transfer processes trigger reactions that finally lead to the oxidation of water, the reduction of NADP+, and the build-up of a proton gradient across the photosynthetic membrane to produce ATP These processes are catalyzed by two membrane-embedded pigment-protein complexes, called... 

The challenge remains to identify more precisely the specific surface chemical arrays on a foreign material which, when it is inserted into the uterine cavity, might trigger reactions that produce these adverse effects as well as inhibit reproductive activities (23). 

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