Localized hydrolysis

The tethering of PKA through AKAPs by itself is not sufficient to compartmentalize and control a cAMP/ PKA-dependent pathway. Cyclic AMP readily diffuses throughout the cell. Therefore, discrete cAMP/PKA signalling compartments are only conceivable if this diffusion is limited. Phosphodiesterases (PDE) establish gradients of cAMP by local hydrolysis of the... 

Vigorous stirring is necessary to prevent caking of the aluminum chloride hydrate and to prevent localized hydrolysis. The checkers found that exactly 7 moles of water gave a somewhat improved yield, but handling was more diflicult. 

The rapid failure as seen in water and acid solution in regions I and II are due to chemical ESC, as discussed before. A plausible explanation of chemical ESC is chain scission caused by the combined action of the high mechanical stress at the (notch) crack tip and chemical attack of the chains due to local hydrolysis. 

Fig. 4.38 (a) Schematic of the patterning via soft lithography on a block copolymer film, (b) AFM friction image acquired on a PS69o-b-PtBA12io film after local hydrolysis by reactive pCP. Reproduced with permission from [69]. Copyright 2007. Wiley-VCH... 

Any bonded phase will exhibit some level of hydrolysis in an aqueous mobile phase. Under most circumstances, the hydrol ed bonded-phase silanol self-adsorbs to the packing. This results in a local hydrolysis equilibrium, which... 

Now the problem is even more complicated not all anions show this typical cation series with activity coefficients increasing from caesium salts to lithium or hydrogen compounds. In Fig. 2(b), just the reverse series is found, and this is not only true for acetate, but also for hydroxide and formate. As early as 1941, Robinson and Harned (see also Robinson and Stokes pp. 423 25) discussed this reversal in the series of ion specificity. They proposed a localized hydrolysis , in which water shares one of its hydrogen atoms with a proton acceptor anion, such as hydroxide... 

Specific Local Anesthetic Agents. Clinically used local anesthetics and the methods of appHcation are summarized in Table 5. Procaine hydrochloride [51-05-8] (Novocain), introduced in 1905, is a relatively weak anesthetic having along onset and short duration of action. Its primary use is in infiltration anesthesia and differential spinal blocks. The low potency and low systemic toxicity result from rapid hydrolysis. The 4-arninobenzoic acid... 

Trimethylsilyl ethers are quite susceptible to acid hydrolysis, but acid stability is quite dependent on the local steric environment. For example, the 17o -TMS ether of a steroid is quite difficult to hydrolyze. 

Binding to Gpy locks the flexible switch regions I and II of Ga into a conformation that firmly binds GDP but is nonproductive for GTP binding and hydrolysis. The replacement of GDP with GTP causes local but dramatic conformational changes to switch regions I and 11, as shown in the Go GTP-yS structure, which disrupt nearly all of the contacts between Gp. and Ga in the switch interface, thereby triggering release of Ga from Gpy (see Figures 13.10 and 13.11). 

The C-C distance in CaC2 is close to that in ethyne (120.5 pm) and it has been suggested that the observed increase in the lanthanoid and actin-oid carbides results from a partial localization of the supernumerary electron in the antibonding orbital of the ethynide ion [C=C] (see p. 932). The effect is noticeably less in the sesquicarbides than in the dicarbides. The compounds EuC2 and YbC2 differ in their lattice parameters and hydrolysis behaviour from the other LnC2 and this may be related to the relative stability of Eu and Yb (p. 1237). 

The importance of occluded cells cannot be overemphasised, and Brown considers that pitting, crevice corrosion, intergranular attack, filiform corrosion and hydrogen cracking are characterised by local acidification due to hydrolysis of metal ions, and that this phenomenon is of major significance in the overall mechanism. 

Phalloidin and phallacidin are cyclic peptides from the mushroom Amanita phalloides that stabilize F-actin. Phalloidin binds to residues 114-118 of an actin protomere and blocks nucleotide exchange without interfering with nucleotide hydrolysis. It enhances the rate of nucleation as well as that of elongation. It slowly penetrates the cell membrane and is used for immunocytochemical localization of F-actin. 

P-Lactamases are enzymes that hydrolyze the P-lactam ring of P-lactamantibiotics (penicillins, cephalosporins, monobactams and carbapenems). They are the most common cause of P-lactam resistance. Most enzymes use a serine residue in the active site that attacks the P-lactam-amid carbonyl group. The covalently formed acylester is then hydrolyzed to reactivate the P-lacta-mase and liberates the inactivated antibiotic. Metallo P-lactamases use Zn(II) bound water for hydrolysis of the P-lactam bond. P-Lactamases constitute a heterogeneous group of enzymes with differences in molecular structures, in substrate preferences and in the genetic localizations of the encoding gene (Table 1). 

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