Acid-enzyme processes

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. 

Glucose/com syrups may be manufactured by either an acid or an acid-enzyme process. Acid-catalyzed hydrolysis was the traditional method of corn syrup production and is still the most common method for producing sweeteners up to about 42 DE. Since acid-catalyzed hydrolysis of sweeteners to 55 DE or above creates products of reversion, such as gentiobiose, isomaltose and trehalose, which give unacceptable flavors to the syrup, these syrups are usually made by acid-enzyme processes.18... 

Although acid hydrolysis is most commonly used to prepare the starting sirup, the liquefying amylase from B. subtilis can be used to thin the initial starch paste without the need for add resistant tanks. The process then becomes an all-enzyme process. The all-enzyme process produces a smaller amount of reversion products than the acid-enzyme process. 

In enzymatic processes, a-amylases, P-amylases, glucoamylases, and pullulanases are used. First, starch liquefaction is conducted with acid, with a-amylase, or with a combination acid/enzyme process. 

Dextrose also may be made by acid-enzyme and enzyme-enzyme systems. In the acid-enzyme process, acid hydrolysis is stopped near 18 D.E. The liquefied slurry is evaporated to 60 percent solids and treated with a fungal glucoamylase until the D.E. is about 90. With the enzyme-enzyme process, a 30 percent starch slurry is liquefied with a heat-stable bacterial amylase followed by treatment with fungal glycoamylase. The liquor is purified in the same manner as used for others." ... 

Enzyme—Heat—Enzyme Process. The enzyme—heat—enzyme (EHE) process was the first industrial enzymatic Hquefaction procedure developed and utilizes a B. subtilis, also referred to as B. amjloliquefaciens, a-amylase for hydrolysis. The enzyme can be used at temperatures up to about 90°C before a significant loss in activity occurs. After an initial hydrolysis step a high temperature heat treatment step is needed to solubilize residual starch present as a fatty acid/amylose complex. The heat treatment inactivates the a-amylase, thus a second addition of enzyme is required to complete the reaction. 

Dual-Enzyme Processes. In some cases, especially in symp production in Europe, a Hquefaction process is used that incorporates both a thermostable enzyme and a high temperature heat treatment. This type of process provides better hydrolyzate tilterabiHty than that attained in an acid Hquefaction process (9). Consequendy, dual-enzyme processes were developed that utilized multiple additions of either B. licheniformis or B. stearothermophilus a-amylase and a heat treatment step (see Eig. 1). 

Com symps [8029-43 ] (glucose symp, starch symp) are concentrated solutions of partially hydrolyzed starch containing dextrose, maltose, and higher molecular weight saccharides. In the United States, com symps are produced from com starch by acid and enzyme processes. Other starch sources such as wheat, rice, potato, and tapioca are used elsewhere depending on avadabiHty. Symps are generally sold in the form of viscous Hquid products and vary in physical properties, eg, viscosity, humectancy, hygroscopicity, sweetness, and fermentabiHty. 

There are two distinct classes of enzymes that hydrolyze nitriles. Nittilases (EC 3.5.5. /) hydrolyze nittiles directiy to corresponding acids and ammonia without forming the amide. In fact, amides are not substrates for these enzymes. Nittiles also may be first hydrated by nittile hydratases to yield amides which are then converted to carboxyUc acid with amidases. This is a two-enzyme process, in which enantioselectivity is generally exhibited by the amidase, rather than the hydratase. 

In the endoplasmic reticulum of eukaryotic cells, the oxidation of the terminal carbon of a normal fatty acid—a process termed ch-oxidation—can lead to the synthesis of small amounts of dicarboxylic acids (Figure 24.27). Cytochrome P-450, a monooxygenase enzyme that requires NADPH as a coenzyme and uses O, as a substrate, places a hydroxyl group at the terminal carbon. Subsequent oxidation to a carboxyl group produces a dicarboxylic acid. Either end can form an ester linkage to CoA and be subjected to /3-oxidation, producing a... 

Glutamates can be produced by fermentation of starches or sugars, but also by breaking the bonds between amino acids in proteins, leaving free amino acids. This process is done by heat or by enzymes it is called hydrolyzing, because the bonds are broken by adding water. 

To break up cellulose/hemicellulose, it is treated physically (milling), with heat, and hydrolyzed (sulfuric acid + enzymes). Also in this case, improved (bio)cata-lytic hydrolysis processes for cellulose/hemicellulose are needed. The sugar can then serve as feedstock for standard fermentation plants. 

The main cyanogenic glycoside in laurel is prunasin, the P-o-glucoside of benzaldehyde cyanohydrin. The enzymic hydrolysis of prunasin may be visualized as an acid-catalysed process, first of all hydrolysing the acetal linkage to produce glucose and the cyanohydrin. Further hydrolysis results in reversal of cyanohydrin formation, giving HCN and benzaldehyde. 

These enzymes mimic the acid-catalysed processes, are commercially available, and may be used just like a chemical reagent. 

The enzymic processes appear exactly equivalent, except that protons are removed and supplied through the involvement of peptide side-chains. It is unlikely that a distinct enolate anion is formed instead, we should consider the process as concerted with a smooth flow of electrons. Thus, as a basic group removes a proton from one part of the molecule, an acidic group supplies a proton at another. 

Ribonuclease II [EC 3.1.13.1], also called exoribo-nuclease II, catalyzes the exonucleolytic cleavage of the polynucleic acid, preferring single-stranded RNA, in the 3 - to 5 -direction to yield 5 -phosphomononucleotides. The enzyme processes 3 -terminal extra-nucleotides of monomeric tRNA precursors, following the action of ribonuclease P. Similar enzymes include RNase Q, RNase BN, RNase PHI, and RNase Y. Ribonuclease T2 [EC 3.1.27.1] is also known as ribonuclease II. 

Trimethoprim acts in the body by interfering with the action of hydrofolate reductase, an enzyme that reduces dihydrofolic acid to tetrahydrofolic acid. This process is necessary for purine biosynthesis of live organisms and DNA, respectively. Reducing the dihydrofolic acid to tetrahydrofolic acid is also catalyzed in humans by dihydrofolate reductase. However, trimethoprim has thousands of more inhibitory effects with respect to bacterial enzymes than with respect of analogons enzymes of mammals, which is the main benefit of trimethoprim. 

This review aims at reporting on the synthesis of aliphatic polyesters by ROP of lactones. It is worth noting that lactones include cyclic mono- and diesters. Typical cyclic diesters are lactide and glycolide, whose polymerizations provide aliphatic polyesters widely used in the frame of biomedical applications. Nevertheless, this review will focus on the polymerization of cyclic monoesters. It will be shown that the ROP of lactones can take place by various mechanisms. The polymerization can be initiated by anions, organometallic species, cations, and nucleophiles. It can also be catalyzed by Bronsted acids, Lewis acids, enzymes, organic nucleophiles, and bases. The number of processes reported for the ROP of lactones is so huge that it is almost impossible to describe aU of them. In this review, we will focus on the more... 

Other drugs are metabolised by Phase II synthetic reactions, catalysed typically by non-microsomal enzymes. Processes include acetylation, sulphation, glycine conjugation and methylation. Phase II reactions may be affected less frequently by ageing. Thus according to some studies, the elimination of isoniazid, rifampicin (rifampin), paracetamol (acetaminophen), valproic acid, salicylate, indomethacin, lorazepam, oxazepam, and temazepam is not altered with age. However, other studies have demonstrated a reduction in metabolism of lorazepam, paracetamol (acetaminophen), ketoprofen, naproxen, morphine, free valproic acid, and salicylate, indicating that the effect of age on conjugation reactions is variable. 

The S-ribonuclease is the complex formed between an eicosapeptide and the S-RNAse. While replacement of various amino acids by fluorinated analogues does not modify the activity of the native complex, replacement of His-12 by 4-F-His has a strong influence. Indeed, the S-ribonuclease, formed between the bovine pancreatic S-RNAse and the fluoro peptide that contains 4-F-His, has no more catalytic activity, but it is stable. This loss of enzymatic activity is probably due to the significant lowering of the pAia of the catalytic His (2.5 units), which results from the presence of the fluorine atom. It is known that histidine plays an important role in nucleophilic and acid-base processes, which are connected to the catalytic activity of numerous enzymes. 

While the amino acid, which has been replaced by its fluorinated analogue, is essential for the functionality of the protein, some biological consequences can occur. Thus, incorporation of 2-F-His into mammalian proteins (4-F-His cannot be incorporated), in cell culture or invivo, is accompanied by inhibition of the induction of several enzymes (e.g., inhibition of acetyltransferase activity of the pineal gland). This probably stems from the formation of defective or inactive enzymes. Indeed, histidine plays an important role in the nucleophilic and acid-base processes connected to the catalytic activity of numerous enzymes. 

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