Non-enzymic hydrolysis

Rate Constants and Activation Parameters for the Non-enzymic Hydrolysis of D-Glucopyranoside at pH 5... 

Mn2+, D.F.P.-ase is further activated by cysteine, histidine, thiolhistidine, and serine, histamine and 2 2 -dipyridyl. Reagents reacting with metal ions, SH groups and carbonyl groups inhibit D.F.P.-ase activity. Work is proceeding on the further elucidation of such mechanisms.1 In a somewhat similar connexion attention is called to the fact that the non-enzymic hydrolysis of D.F.P. is accelerated by heavy metals and their complexes, in particular by copper chelates of ethylene diamine, o-phenanthroline, 2 2 -dipyridyl and histidine.2... 

From the realization of the amphoteric nature of proteins and the importance of [H+] in many of their functions, and as increasing numbers of enzymes were identified, it became commonplace to report their optimum pH. Corrections for non-enzymic hydrolysis of the substrates were usually made but, as was critically reviewed by Dixon and Webb (1959), from many of the results it was not possible to distinguish effects of pH on the protein in general from those on the region actually involved in interaction with the substrate. Nevertheless, many... 

The non-enzymic hydrolysis of phosphates has been extensively studied, as a model for the enzymic processes. Many of the tools developed are applicable equally to enzyme-catalysed and spontaneous processes. 

The following data have been obtained for the non-enzymic hydrolysis of adenosine triphosphate, catalyzed by hydrogen ions ... 

Although it is convincing that metaphosphate ion is not a free intermediate in substitution reactions in aqueous solution, this does not exclude the possibility of reactions of related species proceeding via analogous intermediates. Reactions of thiophosphate monoesters are more rapid than those of phosphate monoesters. If three sulphur atoms replace three of the oxygens of metaphosphate, a stable salt can be isolated (Roesky et al, 1986). Harnett and Lowe (1988) examined the stereochemical course of the non-enzymic hydrolysis of adenosine (P- O, thio) diphosphate in In... 

The primary ionisation of ATP has = 1-2 and the secondary ionisation has p/ 2 = 6.9-7.7. Under physiological conditions, ATP is fully ionised with a charge of 4 as in (11.10), but in cellular functions it is complexed by a variety of cations. ATP-dependent enzymes require a metal atom, usually Mg + for activation (Chapter 11.4). The rate of hydrolysis of ATP is affected by the metal cations present and the latter can also catalyse non-enzymic phosphorylation reactions. In the presence of Cu + or Zn + the rate of non-enzymic hydrolysis of ATP is increased 10-60 fold at pH = 5.0, whereas Mg +, Ba + and Hg + have little effect. 

Structurally related, the non-enzymic hydrolysis products are not as potent pro-inflammatory mediators as the authentic LTB. ... 

More than 30 years ago it was reported that flaxseed homogenates convert 13-HpOTrE into a- and -y-ketols, and the enzyme responsible for this reaction was called hydroperoxide isomerase [54]. Later studies indicated that this reaction was actually a two-step process, consisting of an enzyme-catalysed dehydration of the hydroperoxy fatty acid to a rather unstable allene oxide followed by a non-enzymic hydrolysis [55,56]. The enzyme responsible for allene oxide synthesis has been purified and shown to be a cyt E-450 isoform [57]. As an alternative to hydrolysis, the allene oxide may undergo enzymic cyclization forming 12-oxo-phytodienoic acid. This compound is subsequently converted into jasmonic acid, a phytohormone implicated in the reaction of higher plants to a number of stimuli, such as wounding, fungal elicitation, mechanical forces and osmotic stress [54]. 

Fatty acid diols can be formed via enzymic or non-enzymic hydrolysis of epoxy compounds (see above). In addition, vicinal diols may originate from the isomerization of hydroperoxy fatty acids, which may proceed without the intermediate formation of epoxides [59]. An acetone powder of the red alga Gracilariopsis... 

Fig. 1 shows a typical trace for the kinetics of luciferase luminescence obtained during illumination with arsenate and ADP. The method used to analyze these curves is also shown. The slow, irreversible phase represents ATP-synthesis supported by endogenous phosphate. The rapid phase in the light, and its reversal in the dark, represent light-dependent synthesis, and non-enzymic hydrolysis, respectively, of ADP-arsenate (Slooten, Nuyten 1983). In the steady state these processes are equally rapid, so that... 

Non-enzymic hydrolysis of ADP-arsenate is accelerated by a number of ions, specifically arsenate and Mg (Table II). These data were calculated from log plots of the dark decay of the rapid phase in the luciferase measurements. Similar results were obtained from the ratio VAs/(ADP-As)sg (not shown, see eq. 1). Phosphate has an effect comparable to that of arsenate (not shown) other ions are ineffective. We propose that these effects are due to formation of transient intermediates such as pyro-arsenate or arsenato-pyro-phosphate. These compounds are stable as solids, but not in solution (Dolique 1958). 

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