Enzyme-catalyzed hydrolysis

An example of a biologically important aide hyde is pyridoxal phosphate which is the active form of vitamin Bg and a coenzyme for many of the reac tions of a ammo acids In these reactions the ammo acid binds to the coenzyme by reacting with it to form an imine of the kind shown in the equation Re actions then take place at the ammo acid portion of the imine modifying the ammo acid In the last step enzyme catalyzed hydrolysis cleaves the imme to pyridoxal and the modified ammo acid... 

Cyanogemc glycosides are potentially toxic because they liberate hydrogen cyanide on enzyme catalyzed or acidic hydrolysis Give a mechanistic explanation for this behavior for the specific cases of... 

Knowing how the protein chain is folded is a key ingredient m understanding the mechanism by which an enzyme catalyzes a reaction Take carboxypeptidase A for exam pie This enzyme catalyzes the hydrolysis of the peptide bond at the C terminus It is... 

Alcoholic Fermentation. Certain types of starchy biomass such as com and high sugar crops are readily converted to ethanol under anaerobic fermentation conditions ia the presence of specific yeasts Saccharomyces cerevisia and other organisms (Fig. 6). However, alcohoHc fermentation of other types of biomass, such as wood and municipal wastes that contain high concentrations of cellulose, can be performed ia high yield only after the ceUulosics are converted to sugar concentrates by acid- or enzyme-catalyzed hydrolysis ... 

Both pure L- and D-amino acids can be made using hydantoinase enzymes. These enzymes catalyze the stereoselective hydrolysis of racemic hydantoins such as (50) which is used for the production of D-alanine (15) (58). 

An enzyme-catalyzed appHcation has been used to prepare the enantiomers of hydroxy-substituted tetrahydroisoquinolines (160). The synthesis of ( V)-reticuline [485-19-8] (30) has been reported using similar methodology (161). The substitution of formic acid and paraformaldehyde in this method leads to lower reaction temperatures, freedom from hydrolysis of protective groups, and improved yields (162). 

Oligo- and higher saccharides are produced extensively by acid-and/or enzyme-catalyzed hydrolysis of starch, generally in the form of symps of mixtures (12). These products are classified by thek dextrose equivalency (DE), which is an indication of thek molecular size and is a measure of thek reducing power with the DE value of anhydrous D-glucose defined as 100. 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

The enzyme catalyzes the hydrolysis of an amide bond linkage with water via a covalent enzyme-inhibitor adduct. Benzoxazinones such as 2-ethoxy-4H-3,l-benzoxazin-4-one [41470-88-6] (23) have been shown to completely inactivate the enzyme in a competitive and stoichiometric fashion (Eigure 5). The intermediate (25) is relatively stable compared to the enzyme-substrate adduct due to the electron-donating properties of the ortho substituents. The complex (25) has a half-life of reactivation of 11 hours. 

For the equiUbrium-controUed enzyme-catalyzed peptide synthesis the equiUbrium position Hes far over in the direction of the hydrolysis, and under physiological conditions, the product yield is negligible. The equiUbrium position is deterrnined exclusively by thermodynamic factors and like any other catalysts the enzymes only accelerate the attainment of the equiUbrium. 

Various chemical species influence the rates of hydrolysis of penicillins, e.g. metal ions (Cu >Zn >Ni Co ) (80JCS(P2)1725), carbohydrates (78MI51101), certain amine-containing catechol derivatives (69JPS1102) and /3-cyclodextrin (71JA767). Some of these even show some of the characteristics of enzyme-catalyzed hydrolyses. 

The years that have passed since Sanger determined the structure of insulin have seen refinements in technique while retaining the same overall strategy. Enzyme-catalyzed hydrolysis to convert a large peptide to smaller fragments remains an important... 

Protease inhibitor (Section 28.13) A substance that interferes with enzyme-catalyzed hydrolysis of peptide bonds. 

Enzymes are powerful catalysts. Enzyme-catalyzed reactions are typically 10 to times faster than their uncatalyzed counterparts (Table 16.1). (There is even a report of a rate acceleration of >10 for the alkaline phosphatase-catalyzed hydrolysis of methylphosphate )... 

The glycosidic bond to an anomeric carbon can be either a or (3. Maltose, the disaccharide obtained by enzyme-catalyzed hydrolysis of starch, consists of two cv-D-glucopyranose units joined by a 1->4-o-glycoside bond. Cellobiose, the disaccharide obtained by partial hydrolysis of cellulose, consists of two /3-o-glucopyranose units joined by a 1—>4-/3-glycoside bond. 

The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are biological polymers that act as chemical carriers of an organism s genetic information. Enzyme-catalyzed hydrolysis of nucleic acids yields nucleotides, the monomer units from which RNA and DNA are constructed. Further enzyme-catalyzed hydrolysis of the nucleotides yields nucleosides plus phosphate. Nucleosides, in turn, consist of a purine or pyrimidine base linked to Cl of an aldopentose sugar—ribose in RNA and 2-deoxyribose in DNA. The nucleotides are joined by phosphate links between the 5 phosphate of one nucleotide and the 3 hydroxyl on the sugar of another nucleotide. 

Instead of immobilizing the antibody onto the transducer, it is possible to use a bare (amperometric or potentiometric) electrode for probing enzyme immunoassay reactions (42). In this case, the content of the immunoassay reaction vessel is injected to an appropriate flow system containing an electrochemical detector, or the electrode can be inserted into the reaction vessel. Remarkably low (femtomolar) detection limits have been reported in connection with the use of the alkaline phosphatase label (43,44). This enzyme catalyzes the hydrolysis of phosphate esters to liberate easily oxidizable phenolic products. 

The interest and success of the enzyme-catalyzed reactions in this kind of media is due to several advantages such as (i) solubilization of hydrophobic substrates (ii) ease of recovery of some products (iii) catalysis of reactions that are unfavorable in water (e.g. reversal of hydrolysis reactions in favor of synthesis) (iv) ease of recovery of insoluble biocatalysts (v) increased biocatalyst thermostability (vi) suppression of water-induced side reactions. Furthermore, as already said, enzyme selectivity can be markedly influenced, and even reversed, by the solvent. 

A very attractive and efficient method for the synthesis of L-aminoacids via DKR has been reported by Turner et al. [41a,b]. They employed enzyme-catalyzed ring opening of 5(4H)-oxazolones in combination with a catalytic amount of Et3N. The relatively low pKa of the C-4 proton (8.9) of oxazolones facilitates racemization. Hydrolysis of the ester obtained through DKR, followed by debenzoylation, yields L-aminoacids in excellent enantiomeric excess (99.5%) (Figure 4.16). In their initial studies, they employed Rhizomucor miehei lipase (Lipozyme) as the biocatalyst [41]. More recently, they have obtained excellent results employing CALB [41bj. This method has also been employed by Bevinakatti [41c,d] and Sih [41e,fj. 

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