Molecular mechanics hydrolysis

Sugar is destroyed by pH extremes, and inadequate pH control can cause significant sucrose losses in sugar mills. Sucrose is one of the most acid-labile disaccharides known (27), and its hydrolysis to invert is readily catalyzed by heat and low pH prolonged exposure converts the monosaccharides to hydroxymethyl furfural, which has appHcations for synthesis of glycols, ethers, polymers, and pharmaceuticals (16,30). The molecular mechanism that occurs during acid hydrolysis operates, albeit slowly, as high as pH 8.5 (18). 

J. Pitarch, J. L. Pascual-Ahuir, E. Silla, I. Tunon, V. Moliner, Analysis of a Concerted Mechanism in /3-Lactam Enzymatic Hydrolysis. A Quantum Mechanics/Molecular Mechanics Study , J. Chem. Soc., Perkin Trans. 2, 1999, 1351-1356. 

B. Waszkowycz, I. H. Hiller, N. Gensmantel, D. W. Payling, A Combined Quantum Mechanical/Molecular Mechanical Model of the Potential Energy Surface of Ester Hydrolysis by the Enzyme Phospholipase A2 ,. /. Chem. Soc., Perkin Trans. 2 1991, 225-231. 

In recent years, research on the molecular mechanisms underlying lithium s therapeutic effects has focused on intracellular second messenger generating systems and, in particular, receptor-coupled hydrolysis of phosphoinositide 4,5-biphosphate (PIP2) (Baraban et al. 1989). Lithium, at therapeutically relevant concentrations in the brain, is a potent inhibitor of the intracellular enzyme, inositol monophosphatase [Kj = 0.8 mM), which plays a major role in... 

Gs and other G proteins use a molecular mechanism that involves binding and hydrolysis of GTP (Figure 2-10). This mechanism allows the transduced signal to be amplified. For example, a neurotransmitter such as norepinephrine may encounter its membrane receptor for only a few milliseconds. When the encounter generates a GTP-bound Gs molecule,... 

A concerted rather than a stepwise reaction involving a tetrahedral intermediate is supported for die papain-catalysed hydrolysis of amides. The TS for die hydrolysis has been determined by using a hybrid quantum mechanical/molecular mechanical potential, QM(AM1)/MM.216... 

Hphe molecular mechanism of acid hydrolysis of glycosides is rather well understood today, much confusion being resolved now by the achievements of conformational analysis of carbohydrates (1,2). With regard to the three consecutive steps of reaction (cf. Figure 1)—Le., the formation of a conjugate acid by protonation of either one of the acetalic... 

Ting, T. D., and Ho, Y.-K. (1991). Molecular mechanism of GTP hydrolysis by bovine transducin Pre-steady-state kinetic analyses. Biochemistry 30, 8996-9007. 

Koizumi S, Fujishita K, Tsuda M et al (2003) Dynamic inhibition of excitatory synaptic transmission by astrocyte-derived ATP in hippocampal cultures. Proc Natl Acad Sci USA 100 11023-8 Kubista H, Boehm S (2006) Molecular mechanisms underlying the modulation of exocytotic noradrenaline release via presynaptic receptors. Pharmacol Ther 112 213 42 Kukulski F, Sevigny J, Komoszynski M (2004) Comparative hydrolysis of extracellular adenine nucleotides and adenosine in synaptic membranes from porcine brain cortex, hippocampus, cerebellum and medulla oblongata. Brain Res 1030 49-56 Kurokawa M, Koga K, Kase H et al (1996) Adenosine A2a receptor-mediated modulation of striatal acetylcholine release in vivo. J Neurochem 66 1882-8 Kurz K, von Ktigelgen I, Starke K (1993) Prejunctional modulation of noradrenaline release in mouse and rat vas deferens contribution of PI- and P2-purinoceptors. Br J Pharmacol 110 1465-72... 

Different molecular mechanisms have been separately postulated for dibromo-phakellin [74], dibromoagelaspongin [91], agelastatin [92], mauritiamine [88], and palau amine [78]. A1 Mourabit and Potier proposed a universal chemical pathway, starting from the simple precursors 101 and 140 and leading to over 60 pyrrole-imidazole alkaloids [80]. A new biomimetic spontaneous conversion of proline to 2-aminoimidazolinone derivatives using a self-catalyzed intramolecular transamination reaction together with peroxide dismutation as key step has been described [166]. This work has pointed to dispacamide A as the forerunner of oroidin and compounds 101 and 140 as probable hydrolysis products of oroidin and not the precursors. In this... 

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