Activation energy of hydrolysis

Kasu) et investigated the kinetits and mechanism of surface hydrolysis of P(3HB) with PHA depolymerase from Raktonia pickettii T1 at different reaction temperature and pH. The rate constant of enzymatic hydrolysis increased with a rise in temperature, while the adsorption equilibrium constant decreased. The activation energy of hydrolysis by the catalytic domain calculated from the results obtained was found to be 82kfmor. ... 

Comparison of the rate constants of acid and base hydrolyses shows that kp<< k. This is the result of the difference in activation energies the activation energy of hydrolysis by the OH ion is much lower than that by the hydrogen ion. For the hydrolysis of acetates of aliphatic alcohols, this difference E/ - = 24 U/mol. 

FIGURE 3.8 The activation energies for phosphoryl group-transfer reactions (200 to 400 kj/mol) are substantially larger than the free energy of hydrolysis of ATP ( — 30.5 kj/mol). 

J mol ). This is additional evidence in favor of rate limitation by inner diffusion. However, the same reaction in the presence of Dowex-50, which has a more open three-dimensional network, gave an activation energy of 44800 J mol , and closely similar values were obtained for the hydrolysis of ethyl acetate [29] and dimethyl seb-acate [30]. The activation energy for the hydrolysis of ethyl acetate on a macroreticular sulphonated cationic exchanger [93] is 3566 J mol . For the hydrolysis of ethyl formate in a binary system, the isocomposition activation energy (Ec) [28,92] tends to decrease as the solvent content increases, while for solutions of the same dielectric constant, the iso-dielectric activation energy (Ed) increases as the dielectric constant of the solvent increases (Table 6). 

The calculated activation energy is now 96 kJ mol-1 for die uncatalyzed second-order reaction and 88 kJ mol-1 for the third-order reaction. From hydrolysis data using very low water concentrations (0.005 -0.1 mol-kg-1), the reaction was found to be second order but exhibited a dependence on water concentration in the rate constants (Fig. 3.14). With 1.1 mol - kg 1 water, a combination of second- and third-order reactions was observed with activation energies of 109 and 63 kJ mol-1, respectively.8... 

The hydrolysis of sucrose is a part of the digestive process. To investigate how strongly the rate depends on our body temperature, calculate the rate constant for the hydrolysis of sucrose at 35.0°C, given that k = 1.0 mL-mol -s 1 at 37.0°C (normal body temperature) and that the activation energy of the reaction is 108 kj-mol. ... 

The reaction shows a rather high activation energy of 32.0 kcal.mole . Speculation about the mechanism is worthless until more controlled experiments are performed, taking account of hydrolysis, the role of the reaction Fe(lI)+NH20H, etc. 

Based on a series of studies of the effect of organic solvent on the reaction of Ca-ATPase with Pj and ATP synthesis, De Meis et al. proposed that a different solvent structure in the phosphate microenvironment in Ej and E2 forms the basis for existence of high- and low-energy forms of the aspartyl phosphate [93]. Acyl phosphates have relatively low free energy of hydrolysis when the activity of water is reduced, due to the change of solvation energy. The covalently bound phosphate may also reside in a hydrophobic environment in E2P of Na,K-ATPase since increased partition of Pj into the site is observed in presence of organic solvent [6] in the same manner as in Ca-ATPase. 

As anhydrides, such compounds are subject to spontaneous hydrolysis, which may contribute to detoxification [160]. Thus, soman hydrolysis at pH 7.5 and 37° occurs with a rate constant of 0.003 - 0.004 min-1 and an activation energy of ca. 55 kJ mol 1 [161]. However, most of the published data refer to enzymatic hydrolysis. Enzymes hydrolyzing P-X anhydride bonds are now known as organophosphorus acid anhydrolases (OPA anhydrolases) classified as EC 3.1.8.2 (also known as diisopropyl-fluorophosphatase, DFPase, tabunase, somanase), an activity related to EC 3.1.8.1 (aryldialkyl-phosphatase, paraoxonase, A-esterase) and formerly classified as EC 3.8.2.1 [64] [65] [69], Much public information on these enzymes can be found in [106],... 

The reduction of the rate of hydrolysis due to lowering the temperature 45 C in the solution containing 7 M NH4NO3 is Ah2o/ nh4N03,7m = 4.78, with an activation energy of 5 kcal mol . This solvent is not suitable for low-temperature studies of the lysozyme reaction. 

Kinetic studies of the unnatural 6-a -epimer of ampicillin, fi-ept-ampicillin (154), have revealed an intramolecular process not undergone by ampicillin (or other natural /3-substituted penicillins) At pH 6-9, intramolecular attack of the jS-lactam carbonyl group by the side-chain amino group of (154) yields a stable piperazine-2,5-dione derivative (155). Theoretical calculations show that the intramolecular aminolysis of 6-epi-ampicillin nucleophilic attack occurs from the a-face of the -lactam ring with an activation energy of 14.4kcalmor In other respects, the hydrolysis of the b-a-epimer is unexceptional. 

A new, more general, way to combine ab initio quantum mechanical calculations with classical mechanical free-energy perturbation approach (QM/FE approach) to calculate the energetics of enzyme-catalysed reactions and the same reaction in solution has been reported." The calculated free energies were in fairly good agreement with the experimental data for the activation energies of the first test case, amide hydrolysis in trypsin and in aqueous solution. 

This protein kinase (known as protein kinase A or PK-A) has an R2C2 quaternary structure that binds 3, 5 -cAMP at its dimeric regulatory (R) subunit with resultant release of two catalytic (C) subunits. The free energy of hydrolysis of the cychc nucleotide activator is large (AG 13 kcal/mol) and allows the 3, 5 -cAMP to be virtually irreversibly converted to AMP by the action of a specific phosphodiesterase. This protein kinase, originally discovered by the Nobelists Edwin Krebs and Edward Fischer, is now considered to be the prototype for over two thousand members of the protein kinase superfamily. 

Adachi and Mizushima [30] studied the deposition system DMTC + O2 + H2O in the 400-500 °C temperature range, hi the presence of water vapor, the deposition rate dependence on DMTC concentration increased from [DMTC] to [DMTC]° . They suggested that in the reaction of DMTC + O2, the rate-determining step is the oxidation of Sn-Cl bonds, while in the reaction of DMTC + O2 + H2O, the oxidation of Sn - CH3 bonds is rate determining. As will be seen below, this description of the chemistry is almost certainly incorrect (Sect. 5.2). They also reported an activation energy of 38 kcalmoC for the hydrolysis of DMTC (Fig. 7) and asserted that the hydrolytic decomposition of Sn - Cl bonds is much faster at these temperatures. 

The kinetic parameters above are very similar to those for the hydrolysis of a simple Schiff base, benzalaniline, having an activation energy of 13.2 kcal. and an entropy of activation of about —37 e.u. (40). It appears that the rate determining step for hydrolyses of the complexes is the second step, the splitting off of the aldehyde. Under suitable conditions, the intermediates in such hydrolyses for bis complexes (of Schiff bases derived from ethylenediamine) have been isolated. Only one of the ligands is hydrolyzed, and the nitrogen which had been present in the Schiff base is still coordinated to the central metal (17). 

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