Conversions acid-enzyme

Many products made by fermentation are also based on the conversion of starch. Some examples of the use of enzymatically hydrolyzed starches are the production of alcohol, ascorbic acid, enzymes, lysine, and penicillin. 

In order to improve this reaction, a proper understanding of all parameters affecting product yield is desired. Clearly, the high enzyme consumption is a major obstacle for an efficient and economically feasible process. A likely cause of the inefficient use of DERA in this conversion is enzyme deactivation resulting from a reaction of the substrates and (by-) products with the enzyme. In general, aldehydes and (z-halo carbonyls tend to denature enzymes because of irreversible reactions with amino acid residues, especially lysine residues. From the three-dimensional structure it is known that DERA contains several solvent-accessible lysine residues [25]. Moreover, the complicated reaction profile as shown in Scheme 6.5 indicates the potential pitfalls of this reaction. 

Xanthine oxidase is able to bind allopurinol and catalyze one oxidation, converting it to a compound that is similar to xanthine. However, after that conversion, the enzyme is trapped in an inactive oxidation state and can t carry out its normal function of forming uric acid. Additionally, allopurinol inhibits the de novo ( new, from other compounds not recycled) synthesis of purines, further decreasing the amount of uric acid formed in the blood. 

Maltodextrins may be manufactured either by acid or by acid-enzyme processes. Maltodextrins produced by acid conversion of starch from dent com contain a high percentage of linear fragments, which may slowly reassociate into insoluble compounds causing haze in certain applications. 

Starch conversion refers to the process of converting starch into other products. It involves gelatinization, liquefaction, and saccharification. Liquefaction refers to the acid-or enzyme-catalyzed conversion of starch into maltodextrin. Starch, usually from wet milling of com, is pumped in a slurry to the conversion plant, where it undergoes one or more hydrolytic processes to yield mixtures of various carbohydrates in the form of syrups. The kind and amount of the various carbohydrates obtained depend upon the type of hydrolysis system used (acid, acid-enzyme, or enzyme-enzyme), the extent to which the hydrolytic reaction is allowed to proceed, and the type of enzyme(s) used. The fact that most starches consist of two different kinds of polymers... 

Fig. 5.—Process and Conditions for the Manufacture of Dual-conversion (Acid- and Enzyme-Catalyzed Hydrolyses) Com Syrups.

Methylaspartase also catalyzes the reversible addition of ammonia to ( )-2-butenedioic, and (Z)-2-chloro- and (Z)-2-bromo-2-butenedioic acid (ammonium salts) 39 40a b. During the bro-mo-2-butenedioate conversion the enzyme became inactive and the aminated product rapidly cyclized to give the aziridine. 

Decreased purine salvage conversion of bases to uric acid enzyme is completely absent in Lesch-Nyhan syndrome... 

Conversion Acid Acid Acid Acid enzyme ... 

Olivieri, R., Fascetti, E., Angelini, L. Degen, L., Enzymatic conversion of N-carbamyl-D-amino acids to D-amino acids. Enzyme Microb. TechnoL, 1 (1979) 201-... 

Incubation of a transaminase with its amino acid substrate, in the absence of an amino acceptor, initiates conversion of enzyme-PLP to enzyme-pyridoxamine-P. The pyridoxamine-P form of many transaminases dissociates to yield the apoenzyme much more readily than does the PLP form, and phosphate ions are known to facilitate removal of the cofactor from the apoenzyme (cf. Braunstein, 1973). Some plant aminotransferases, however, appear to resolve only incompletely after incubation with the amino acid substrate (Unger and Hartmann, 1976). There are a very few cases where a partially purified enzyme has shown strict PLP dependence, even though no deliberate attempt at cofactor removal was made (Abbadi and Shannon, 1969 Hatch, 1973). 

Current industrial applications of enzymes include the preparation of modified penicillins using penicillin acylase, and the conversion of starch into sugars [7]. Because of their ability to digest fatty acids, enzymes saw a fleeting popularity in household detergents, although they are now less common. 

The observation that fumaric acid was a product of the interaction of citrulline with aspartate, and the fact that the rate curves showed an induction period, suggesting accumulation of an intermediate, implied that two enzymatic steps were involved in the conversion. One enzyme catalyzes the ATP-utilizing condensation of citrulline with aspartate to form... 

A second approach to efficient synthesis of gluconic acid and sorbitol has been the use of cell-free GFOR from Z. mobilis. Using a crude extract of Z. mobilis in a continuous ultrafiltration membrane reactor, excellent substrate conversion and enzyme stability were maintained for about 10 days (Silva-Martinez et al. 1998). However, it has been concluded that the strict requirements for enzyme stability would be costly for commercial production and downstream processing, which is a strong argument favoring use of permeable cells (Nidetzky et al. 1997). 

Treatment of starch with acids, enzymes or oxidizing agents (such as sodium hypochlorite) are commonly used to reduce the molecular weight of starch and thus decrease the viscosity and modify the gelling properties of aqueous starch dispersions. Starches that have been partially depolymerized by acids or enzymes are commonly referred to as dextrins. Conversely, the swelling and solubility of starch granules can be reduced by cross-linking. 

Another example of a nitrile conversion without enzyme specification is the biotransformation of (i ,5)-3-phenyllactonitrile (phenylacetaldehyde cyanohydrin) to (5)-3-phen-yUactic acid, a precursor for the synthesis of pharmacophores including renin inhibitors, protease inhibitors, and anti-HIV reagents, by Pseudomonas sp. BC-18 [19]. The enantiomeric excess of 75% after biotransformation was increased to 99.8% by repeated crystallization, and the production was enhanced by the addition of 2% (w/v) CaCl2 to the reaction mixture for the precipitation of the (5)-acid. In a mutant strain, the specific activity and the final accumulation were enhanced 16- and 1.2-fold, respectively, compared to the parent strain. A product yield of 70% after biotransformation was obtained due to the... 

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