Enzyme thermal

The maj ority of these new plants are corn dry-grind ethanol plants. Approximately 2.5-2.7 gal of ethanol, 17.5 lb of dried distiller s grain (DDG), and 17 lb of carbon dioxide are produced from each bushel of corn processed through a corn dry mill (2). Since 1980, process improvements in enzymes, thermal-tolerant yeasts, molecular sieves, and cogeneration have achieved a 50% reduction in the energy required to produce ethanol from corn (2). Further improvements in efficiencies and reductions in production costs can be expected in the future. 

The effect of the substrate (benzonitrile) concentration on nitrile hydratase activity was investigated in a CSMR in the range of 2-10mM at low temperature (10 °C) in order to reduce the enzyme thermal inactivation as much as possible. The experimental runs are illustrated in Figure 17.4a as a semi-logarithmic plot of the specific reaction rate against process time. Both the r - and the ka-values were calculated (as summarized in the previous paragraph) and are quoted in Table 17.1. 

The metliylenetetraliydrofolate reductase enzyme reduces 5,10-methylenetetrahydrofolate to form 5-methyltetrahy-drofolate, which provides methyl groups necessary for homocysteine remetliylation to methionine. The severity of the enzyme defect and of clinical symptoms varies considerably. Completely absent enzyme activity results in neonatal apneic episodes, myoclonus leading to coma, and death, whereas partial deficiency may result in mental retardation and seizures. Premature cardiovascular disease or peripheral neuropathy could be the only manifestation. A common polymorphism (677C>T) is associated with enzyme thermal lability and mild elevation of homocysteine in the presence of folate insufficiency, implicating a risk for both vascular disease and neural tube defects. ... 

The oxidation of 3-pentadecylcatechol in various solvents has been studied under aerobic conditions (ref. 327). The enzymic, thermal and oxidative reactions leading to the polymerisation of urushiol have been examined (ref. 328). Many other papers presented at the 1993 symposium on oriental lacs have been concerned with the same problem. 

The enzyme was stable for 10 min up to 45°C, whereas the activity decreased rapidly to 30% after 10 min at 55°C (Fig. 2). The temperature maximum (Tmax) was found to he 47°C under the conditions tested (30 min endpoint assays), whereupon activity rapidly diminished, possibly because of enzyme thermal instability. 

Stability is not related to activity and in many cases they have opposite trends. It has been suggested that there is a trade-off between stability and aetivity based on the fact that stability is clearly related to moleeular stiffening while eonforma-tional flexibility is beneficial for catalysis. This can be clearly appreciated when studying enzyme thermal inactivation enzyme activity increases with temperature but enzyme stability decreases. These opposite trends make temperature a critical variable in any enzymatic process and make it prone to optimization. This aspect will be thoroughly analyzed in Chapters 3 and 5. 

Enzyme Reactor Design and Performance Under Non-Modulated and Modulated Enzyme Thermal Inactivation... 

Enzyme thermal inactivation during bioreactor operation is of paramount importance and must be considered for proper bioreactor design, as shown in Fig. 3.1. To do so, a mathematical model must be developed based on experimentally calculated and validated parameters. Mechanistic models to describe enzyme inactivation were presented in sections 5.4.1 and 5.4.2. 

Enzyme thermal stability in the PE presence. This technique allows us to know the melting temperature of a macromolecule (Tj ), the temperature where 50 % is in native form and 50 % is in its denatured form. Also, the enthalpy and entropic changes of the denaturalization process can be calculated in this way. The information given by this technique is useful in the sense that it allows us to determine whether the PE presence increases o decreases the thermal stability of an enzyme [38]. 

Craig D B, Arriaga E A, Wong J C Y, Lu H and Dovichi N J 1996 Studies on single alkaline phosphatase molecules reaction rate and activation energy of a reaction catalyzed by a single molecule and the effect of thermal denaturation—the death of an enzyme J. Am. Chem. See. 118 5245-53... 

Theovent The 0x0 process Therapeutic agents Therapeutic enzymes Therapeutic lenses Therapeutic role Therbar Therm-8 Thermal analysis... 

Phosphatase Test. The phosphatase [9001-78-9] test is a chemical method for measuring the efficiency of pasteurization. AH raw milk contains phosphatase and the thermal resistance of this enzyme is greater than that of pathogens over the range of time and temperature of heat treatments recognized for proper pasteurization. Phosphatase tests are based on the principle that alkaline phosphatase is able, under proper conditions of temperature and pH, to Hberate phenol [108-95-2] from a disodium phenyl phosphate substrate. The amount of Hberated phenol, which is proportional to the amount of enzyme present, is determined by the reaction of Hberated phenol with 2,6-dichloroquinone chloroimide and colorimetric measurement of the indophenol blue formed. Under-pasteurization as well as contamination of a properly pasteurized product with raw milk can be detected by this test. 

Binders. Paper-coating biaders are either polymers derived from aatural sources or syathetic polymers. The largest volume, aaturally derived biader is starch (qv) (99). Starch is provided ia derivatized form or unmodified form pead com starch is used predomiaanfly for the latter. Unmodified starch is solubilized by thermal conversion or enzyme conversion. The most common derivatized products are acetylated [9045-28-7] oxidized, and hydroxyethylated starches. 

Low temperature Dual enzyme, dual heating Dual enzyme, single heating Thermal liquefaetion... 

ThermalLkjucfaction Process. In the thermal Hquefaction process (see Eig. 1), a starch slurry containing no enzyme or added calcium is heated for several minutes. The slurry is slightly acidic and sufficient acid Hquefaction is achieved to reduce viscosity. The hydrolyzate (at essentially zero DE) is flash-cooled to 95—100°C, a-amylase is added, and the pH is adjusted. The reaction then goes to completion. 

Effect of Temperature and pH. The temperature dependence of enzymes often follows the rule that a 10°C increase in temperature doubles the activity. However, this is only tme as long as the enzyme is not deactivated by the thermal denaturation characteristic for enzymes and other proteins. The three-dimensional stmcture of an enzyme molecule, which is vital for the activity of the molecule, is governed by many forces and interactions such as hydrogen bonding, hydrophobic interactions, and van der Waals forces. At low temperatures the molecule is constrained by these forces as the temperature increases, the thermal motion of the various regions of the enzyme increases until finally the molecule is no longer able to maintain its stmcture or its activity. Most enzymes have temperature optima between 40 and 60°C. However, thermostable enzymes exist with optima near 100°C. 

Subtilisins are a group of serine proteinases that are produced by different species of bacilli. These enzymes are of considerable commercial interest because they are added to the detergents in washing powder to facilitate removal of proteinaceous stains. Numerous attempts have therefore recently been made to change by protein engineering such properties of the subtilisin molecule as its thermal stability, pH optimum, and specificity. In fact, in 1988 subtilisin mutants were the subject of the first US patent granted for an engineered protein. 

Like most chemical reactions, the rates of enzyme-catalyzed reactions generally increase with increasing temperature. However, at temperatures above 50° to 60°C, enzymes typically show a decline in activity (Figure 14.12). Two effects are operating here (a) the characteristic increase in reaction rate with temperature, and (b) thermal denaturation of protein structure at higher tem-... 

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