Enzymatic reactions temperature effect

The overall effect of temperature on reaction rates is a combination of the effects produced at each stage. In general, a 10 °C increase in T will double the rate of an enzymatic reaction. Temperature control to within 0.1 °C is necessary to ensure the reproducible measurement of reaction rates. Temperatures <40 °C are generally employed, to avoid protein denaturation. 

FIGURE 14.12 The effect of temperature on enzyme activity. The relative activity of an enzymatic reaction as a fnncdon of tempera-tnre. The decrease in the activity above 50 C is dne to thermal denatnradon. 

Here, the temperature effect is discussed from the aspect of synthetic utility. Temperature control of enantioselectivity, i.e., the low-temperature method , is simple and now practically acceptable method. The phenomenon is based on the theory of physical organic chemistry and will be studied further for understanding the enzymatic reaction as organic reaction. 

Kinetic complexity definition, 43 Klinman s approach, 46 Kinetic isotope effects, 28 for 2,4,6-collidine, 31 a-secondary, 35 and coupled motion, 35, 40 in enzyme-catalyzed reactions, 35 as indicators of quantum tunneling, 70 in multistep enzymatic reactions, 44-45 normal temperature dependence, 37 Northrop notation, 45 Northrop s method of calculation, 55 rule of geometric mean, 36 secondary effects and transition state, 37 semiclassical treatment for hydrogen transfer,... 

Kinetic analysis was used to characterize enzyme-catalyzed reactions even before enzymes had been isolated in pure form. As a rule, kinetic measurements are made on purified enzymes in vitro. But the properties so determined must be referred back to the situation in vivo to ensure they are physiologically relevant. This is important because the rate of an enzymatic reaction can depend strongly on the concentrations of the substrates and products, and also on temperature, pH, and the concentrations of other molecules that activate or inhibit the enzyme. Kinetic analysis of such effects is indispensable to a comprehensive picture of an enzyme. 

Temperature and moisture are two of the most important environmental variables that affect microbial growth, survival, and activity. At optimal temperature and moisture conditions, chemical and enzymatic reactions in the cell will occur the most rapidly and growth and activity will be the highest. However, below and above these optimal conditions, microbial activity decreases. The microbial degradation of. v-triazines appears to follow the same pattern. The effect of soil moisture and temperature on the degradation of terbutryn was evaluated by Chu-Huang et al. (1975). They reported that after 20 weeks of incubation above 10°C and at 14% soil moisture, phytotoxic levels of terbutryn to wheat were not detected in Teller sandy loam soil. 

The rate of an enzymatic reaction is affected by a number of environmental factors, such as solvent, ionic strength, temperature, pH, and presence of inhibitor/activator. Some of these effects are described below. 

The effect of temperature satisfies the Arrhenius relationship where the applicable range is relatively small because of low and high temperature effects. The effect of extreme pH values is related to the nature of enzymatic proteins as polyvalent acids and bases, with acid and basic groups (hydrophilic) concentrated on the outside of the protein. Finally, mechanical forces such as surface tension and shear can affect enzyme activity by disturbing the shape of the enzyme molecules. Since the shape of the active site of the enzyme is constructed to correspond to the shape of the substrate, small alteration in the structure can severely affect enzyme activity. Reactor s stirrer speed, flowrate, and foaming must be controlled to maintain the productivity of the enzyme. Consequently, during experimental investigations of the kinetics enzyme catalyzed reactions, temperature, shear, and pH are carefully controlled the last by use of buffered solutions. 

The most common enzymatic reactions are those with two or more substrates and as many products. But many of the simpler single-substrate schemes are valuable for the development of kinetic ideas concerning effects of pH, temperature, etc., on enzyme reaction rates. Although the mechanisms of multisubstrate reactions are complicated, their kinetics can often be described by an equation of the form ... 

The effect of varying reaction temperature and substrate molar ratio at constant reaction time (12h), enzyme amount (30%), and added water content (10%) is shown in Figure 9.1. In general, an increase in substrate molar ratio led to lower yields at any temperature. It was concluded that a great deal of methanol inactivated Novozym 435 to synthesize the biodiesel. Similar results, that an excess of methanol decreased the enzymatic biodiesel catalyzed by Lipozyme IM77, was reported by our previous study (Shieh et al., 2003). 

The rate of an enzymatic reaction is proportional to its reaction temperature. For most enzymatic reactions, values of Qio (the relative reaction rates at two temperatures differing by 10 °C) vary from 1.7 to 2.5. However, an increase in the rate of the catalyzed reaction is not the only effect of increasing temperature on an enzymatic reaction. In theory, the initial rate of reaction measured instantaneously wiU increase with a rising temperature, hi practice, however, a... 

The formation of typical cheese flavours during natural ripening processes are not fully understood yet. The majority of reactions last for an extended time period (months) and comprise oxidative, inter- and intramolecular, enzymatic or microbial (cf. blue cheese) reactions. Substrates are partially very reactive milk-based ingredients which are mainly transformed to volatile flavour intensive compounds like esters, methylketones, aldehydes, lactones and sulphur containing products. The effect of enzymes on the flavour enhancement is also not fully understood. By variation of lipase dosage, reaction time and reaction temperature the production of different flavour notes from milk and butterfat is possible. 

Holmes et al. reported the first enzyme catalyzed reactions in water-in-CO2 microemulsions (67). Two reactions, a lipase-catalyzed hydrolysis and a lipoxygenase-catalyzed peroxidation, were demonstrated in water-in-C02 microemulsions using the surfactant di(l/7,l/7,5/7-octafluoro- -pentyl) sodium sulfosuccinate (di-HCF4). A major concern of enzymatic reactions in CO2 is the pH of the aqueous phase, which is approximately 3 when there is contact with CO2 at elevated pressures. Holmes et al. examined the ability of various buffers to maintain the pH of the aqueous solution in contact with CO2. The biological buffer 2-(A-morpholino)ethanesulfonic acid sodium salt (MES) was the most effective, able to maintain a pH of 5, depending on the pressure, temperature, and buffer concentration. The activity of the enzymes in the water-in-C02 microemulsions was comparable to that in a water-in-heptane microemulsion stabilized by the surfactant AOT, which contains the same head group as di-HCF4. 

It is clear that the evidence for vicinal hydration of macromolecules in solution may be indirect or circumstantial, but it cannot be readily dismissed. A vast literature exists on the effects of temperature on rates of enzymatic reactions. It is our view that in many cases, where sufficiently closely spaced data are available, distinct changes in the rate of enzymatic reactions occur at or very near 15°, 30°, 45°, and 60°C. It thus seems reasonable to assume that vicinal water is present and manifests its existence by affecting the rates of the reactions. For a fuller discussion of the evidence for the occurrence of kinks in enzymatic rate data, see Drost-Hansen (1971, 1973) and Etzler and Drost-Hansen (1979). 

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