Non-enzymatic

Chorismate Mutase catalyzed Claisen Rearrangement- 10 rate enhancement over non-enzymatic reaction... 

Non-enzymatic cyclizations of educts containing chiral centres can lead to products with additional "asymmetric centres. The underlying effect is called "asymmetric induction . Its systematic exploration in steroid syntheses started when G. Saucy discovered in 1971 that a chiral carbon atom in a cyclic educt induces a stereoselective Torgov condensation several carbon atoms away (M. Rosenberger, 1971, 1972). 

These are major disadvantage of the esterase resolution process. Since die optimum pH of die enzymic reaction is generally on the alkaline side, die esters used as substrates are non-enzymatically hydrolysed and die optical purity of die L-amino adds obtained is generally low. Also the substrate has to be protected at the amino group in most cases in order to prevent formation of diketopiperasines. The esterase method is not attractive in practice and to the best of our knowledge is not used on an industrial scale. 

Many procedures have been suggested to achieve efficient cofactor recycling, including enzymatic and non-enzymatic methods. However, the practical problems associated with the commercial application of coenzyme dependent biocatalysts have not yet been generally solved. Figure A8.18 illustrates the continuous production of L-amino adds in a multi-enzyme-membrane-reactor, where the enzymes together with NAD covalently bound to water soluble polyethylene glycol 20,000 (PEG-20,000-NAD) are retained by means of an ultrafiltration membrane. 

Cormier, M. J., and Dure, L. S. (1963). Studies on the bioluminescence of Balanoglossus biminiensis extracts. I. Requirement for hydrogen peroxide and characteristics of the system. J. Biol. Chem. 238 785-789. Cormier, M. J., and Hori, K. (1963). Studies on the bioluminescence of Renilla reniformis. IV. Non-enzymatic activation of Renilla luciferin. Biochim. Biophys. Acta 88 99-104. 

Shimomura, O., Satoh, S., and Kishi, Y. (1993b). Structure and non-enzymatic light emission of two luciferin precursors isolated from the luminous mushroom Panellus stipticus. J. Biolumin. Chemilumin. 8 201-205. 

Non-enzymatic activation of molecular nitrogen. G. Henrici-Olive and S. Olive, Angew. Chem., Int. Ed. Engl., 1969, 8, 650-659 (47). 

An interesting combination of enzymatic with non-enzymatic transformation in a one-pot three-step multiple sequence was reported by Waldmann and coworkers [82]. Phenols 125 in the presence of oxygen and enzyme tyrosinase are hydroxylated to catechols 126 which are then oxidized in situ to ortho quinones 127. These intermediates subsequently undergo a Diels-Alder reaction with inverse electron demand by reaction with different dienophiles (Table 4.19) to give endo bicyclic 1,2-diketones 128 and 129 in good yields. 

Bellemin-Laponnaz S, Twedel J, Ruble JC, Breitling FM, Fu GC (2000) The kinetic resolution of allylic alcohols by a non-enzymatic acylation catalyst application to natural product synthesis. Chem Conunun 1009-1010... 

Enzymes are exceptionally efficient catalytic proteins which increase the speed of a chemical reaction without themselves undergoing a permanent change. Under optimal conditions, most enzymatic reactions proceed from 10 to 10 times more rapidly than the corresponding non-enzymatic reactions. For example, one molecule of catalase, the enzyme which converts hydrogen peroxide into water and atomic oxygen, is able to deal with approximately 5 million molecules of H2O0 per minute. 

Solberg and co-workers have applied discriminate analysis of clinical laboratory tests combined with careful clinical and anatomic diagnoses of liver disease in order to determine which combinations of the many dozen liver diagnostic tests available are the bes t ( ). These authors found that the measurement of GPT, GMT, GOT, ALP and ceruloplasmin were the most useful enzymatic tests, when combined with other non-enzymatic tests such as the measurement of bilirubin, cholesterol, hepatitis-B associated Australian antigen, etc. Another group of highly useful enzymes, not discussed in this review, are those clotting factors and the enzyme cholinesterase which are synthesized by the liver cells. 

D. Coenzyme A.—Succinyl phosphate (42) reacts rapidly and non-enzymatically with CoA in the pH range 3—8 to yield succinyl CoA (43). This reaction is dependent on the presence of a suitably situated free carboxy-group as such nucleophilic attack at carbon is not known with other acyl phosphates. Moreover, maleyl phosphate reacts rapidly with CoA while fumaryl phosphate fails to react under the same conditions. Hence the formation of a cyclic intermediate (44) from succinyl phosphate is... 

MANZOCCO L, CALLiGARis s, MASTROCOLA D, NicoLi M c and LERici c R (2001) Review of non-enzymatic browning and antioxidant capacity in processed foods . Trends Food Sci Technol, 11 340-6. 

According to Kruger s original hypothesis to explain methyl-ation of rat liver DNA following administration of NDPA, NMPA should be formed from NOPPA. NOPPA is converted into NMPA in a base-catalyzed, non-enzymatic reaction, but this takes place only at high pH (16). We observed no detectable reaction at physio-... 

The second pathway is the eccentric cleavage that occurs at double bonds other than the central 15,15 -double bond of the P-carotene molecule to produce different products called P-apocarotenals with various chain lengths. Because only trace amounts of apocarotenals were detected in vivo from tissues of animals fed P-carotene and these compounds can be formed non-enzymatically from P-carotene auto-oxidation, the existence of this pathway was controversial until recently. The identification of P-carotene 9, 10 -oxygenase (BC02), which acts specifically at the 9, 10 double bond of P-carotene to produce P-apo-lO -carotenal and P-ionone, provided clear evidence of the eccentric cleavage pathway in vivo. Lycopene was also reported as a substrate for BC02 activity. 

For practical applications of HNLs as catalysts for the preparation of chiral cyanohydrins, three objectives have been achieved first, to get high enantioselec-tivity it is decisive to suppress the non-enzymatic addition of HCN to the substrate ... 

Sies, 1993). One might reasonably conclude, therefore, that it is unlikely that non-enzymatic lipid peroxidation could have any role to play in human disease (Father et al., 1990). 

Ascorbate is known to act as a water-soluble antioxidant, reacting rapidly with superoxide, hydroxyl and peroxyl radicals. However, reduced ascorbate can react non-enzymatically with molecular oxygen to produce dehydroascorbate and hydrogen peroxide. Also, ascorbate in the presence of light, hydrogen peroxide and riboflavin, or transition metals (e.g. Fe, Cu " ), can give rise to hydroxyl radicals (Delaye and Tardieu, 1983 Ueno et al., 1987). These phenomena may also be important in oxidative damage to the lens and subsequent cataract formation. 

GSHPx, CAT and SOD, which normally protect cells from free-radical damage have not been detected in aqueous humour. It has therefore been su ested that damage by free radicals and hydrogen peroxide to the anterior segment is prevented by a non-enzymatic extracellular oxidoreduction system involving a constant supply of reduced glutathione to the aqueous fluid from the ciliary epithelium, cornea and lens (Riley, 1983). 

Abraham, E.C., Swarmy, M.S. and Perry, R.E. (1989). Non-enzymatic glycation of lens crystallins in diabetes and ageing. Prog. Clin. Biol. Res. 304, 123-139. 

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