Cascade mechanism

Stimulation of glycogen breakdown involves consumption of molecules of ATP at three different steps in the hormone-sensitive adenylyl cyclase cascade (Figure 15.19). Note that the cascade mechanism is a means of chemical amplification, because the binding of just a few molecules of epinephrine or glucagon results in the synthesis of many molecules of cyclic / MP, which, through the action of c/ MP-dependent protein kinase, can activate many more molecules of phosphorylase kinase and even more molecules of phosphorylase. For example, an extracellular level of 10 to 10 M epinephrine prompts the for-... 

Electron impact studies10 of the appearance potentials and reaction cross-sections for the decomposition of W(CO)6 have shown that this decomposition occurs by a cascade mechanism... 

Fig. 2. A possible protease cascade mechanism for extracellular degradation and metastasis. Active proteases are shown in boxes with dark background, while inhibitors are shown in boxes with light background. Reproduced with permission from Schmitt et al.. Fibrinolysis, copyright 1992...

Tlie initiator caspases receive proapoptotic signals and initiate the activation of a caspase cascade. Tliey are activated by an interaction with a transmembrane receptor or by cytotoxic influences. A complex is thus formed known as the apoptosome (see 15.4). The effector caspases are activated by an upstream caspase via a cascade mechanism. They are the component that executes apoptosis, initiates degradation of central proteins and directs the cell to death. 

The effect of a regulated change in the activity of an enzyme is often amplified through a cascade mechanism. The first enzyme acts on a second enzyme, the second on a third, etc. The effect is to rapidly create a large amount of the active form of the last enzyme in the series. 

Computer simulations as well as studies of experimental models have led to the following conclusions.343 311 Even simple cascade mechanisms, such as the one shown in Fig. 11-10, can provide a more flexible response... 

Complement is a group of more than 30 proteins found in blood serum, which are activated in a cascade mechanism when antibody and antigen com-bine10/111/142 148 (Eq. 31-1). This classical pathway for activation of complement is outlined in Fig. 31-8. The proteins involved in the cascade are designated Cl to C9. Many of them undergo proteolytic cleavage, the... 

Activated Clr (often designated Clr but here and in Fig. 31-8 as Clr) is one of five different serine proteases involved in activation of complement.156 The substrate for the trypsinlike Clr is Cls, a proenzyme which is converted by the action of Clr into another trypsinlike serine protease Cls.157 160 Through a rather elaborate cascade mechanism, depicted in Fig. 31-8, the important proenzyme C2 is activated.161 Its active form C2a is a serine protease, which cleaves proteins C3 and C5 to the active forms C3b and C5b. Protein C4 is also cleaved to C4b by activated Cl. C4 and C3 are also activated, and protein C5 is cleaved... 

The complement system is a humoral effector of inflammation which is activated by a cascade mechanism through the classical and/or alternative pathway [62]. Activation of the system is normally beneficial for the host. However, excessive activation may evoke pathological reaction in a variety of immunological and degenerative diseases and hyperacute rejection in transplantation. Therefore, the modulation of complement activity should be useful in the therapy of inflammatory diseases. 

Branching due to the chain transfer of a side group of a polymer is easily described in the cascade mechanism by introducing a third functional group which may react with another monomer with probability y. Instead of Eq. (E.l), one now has106,107 ... 

This theory thus suggests a pharmacological cascading mechanism, whereby the SSRls exert their therapeutic actions, namely, powerful disinhibition of serotonin... 

The good agreement between our model calculations and our experimental result shows that we have a quantitative understanding of the mechanism of MChA i photoresolution. For the case considered here, the cascading mechanism does nol contribute significantly. However, in other systems, in particular in those consist... 

Both the thermally and the photochemically initiated extrusion of nitrogen from bicyclic diazene (1) leads to the formation of a 1,3-diradical (diyl) which is structurally related to trimethylenemethane. As shown in the cascade mechanism illustrated, two forms of the diyl can be intercepted by alkenes bearing electron-withdrawing groups (diylophiles), viz. the open form of the singlet diyl and the triplet diyl which is formed via intersystem crossing from the singlet (Scheme 1). ... 

More recently an alternative biosynthetic pathway has been proposed by Townsend and Basak (Scheme 22) [83]. This alternative model involves the iterative syn-oxidative cyclization of a (Z,Z,Z)-triene intermediate 44 in contrast to the (E,E,E)-triene intermediate 42 of the epoxide cascade mechanism. The putative, alkoxy-linked, non-heme metal-oxo species 45 undergoes a [2-1-2] cycloaddition to yield the metalloxetane intermediate 46. Reductive elimination then results in an overall syn-addition of the two oxygen atoms 47. Oxidation of the metal intermediate 47 to 48 and two further [2 + 2] cycloaddition-reductive elimination-metal oxidation cycles would result, after final hydroxylation, in monensin A 41. 

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