Q10 values

The ratio of rate constants of a reaction at two temperatures 10°C apart is called the Q10 value of the reaction. This ranges from 1.7 to 2.5 in enzyme-catalysed reactions. 

Figure 7.4. Temperature compensation of LDH (upper panel) and citrate synthase (CS) (lower panel) activity in brains of Antarctic notothenioid fishes and tropical fishes. Enzymatic activity in homogenates of brain was measured at a common temperature, 10°C, and extrapolated to the approximate habitat temperatures of the species (0°C for Antarctic fish and 25°C for tropical species) using experimentally determined Q10 values. Activities at habitat temperatures are indicated in the figure. Despite substantial temperature compensation, an approximately twofold difference in activity persists at habitat temperatures for both enzymes. (Data from Kawall et al., 2001).

Q10 values may be calculated easily by determining the extinction time at two temperatures differing exactly by 10°C. Then ... 

Since the measurement of serum T3 and T4 concentrations may not be helpful, an alternative would be to measure metabolic status. Measurement of the serum concentration of co-enzyme Q10 may distinguish patients with clinical thyroid dysfunction from those who simply have abnormalities of thyroid function tests (49), but the value of this test remains to be established. 

The kinetic parameters 2-value and the related Q10 coefficient (Q10 = 1010/z) reflect the temperature dependence of the denaturation phenomenon (decrease in fluorescence intensity). The 2-value is the interval of temperature required to change the D-value by a factor of 10. 

For every temperature and buffer, the corresponding D-values at pH between 6.0 and 8.5 were calculated from the set equations shown in Table 2. The respective 2-values (°C), were determined from the negative reciprocal of the slopes of the regression lines of the relations between Log10 D-value and corresponding temperatures. The Q10 coefficients were estimated through the relation to 2-values (Q10 = 10(10/z)) those parameters are given in Table 3. 

Meanwhile, the process coefficient Q10 (Q10 = 1010/z) of about 3.0 suggested that acetate and Tris-HCl buffers at pH 7.0 provided similar stabilization for the protein s thermal characteristics greater than phosphate (Qio= 3.99), whose system exposed GFPuv to more dependence on temperature change. At pH 8.0, the protein in Tris-HCl was confirmed to exhibit greater stability than in phosphate, when the D-values decreased, respectively, four and five times for every 10°C increase in heating temperature. 

For pH > 7.0, the Q10 > 5.0 coefficient showed D-values 13% more vulnerable for GFPuv in phosphate than in Tris-HCl and acetate buffers, confirming its role in the improved maintenance of GFPuv conformation and fluorophore emission output. 

Fructan fructan fructosyl transferase has a molecular weight of approximately 70 kDa and can be separated into five species with pH values between 4.5 and 5.0. The enzyme has a pH optimum for fructosyl transfer activity between 5.5 and 7.0 and a temperature optimum in the 25 to 35°C range. Like 1-SST, 1-FFT has a low Q10 (i.e., 1.14 between 25 and 5°C), indicative of its ability to function at relatively low temperatures (Koops and Jonker, 1994). The rate of transfer of fructosyl groups increases with substrate concentration up to 100 mol nr3. 

Most enzymes show a 50-300% increase in reaction rate when the temperature is increased by 10°, and the ratio of rate constants at two temperatures 10° apart is usually between 1.5 and 4.0 for most enzymes. This value is termed Q10 and is derived from the Arrhenius equation [Equation (5.9)], which can be integrated to give... 

Fmax at light saturation and at the optimal temperature for photosynthesis varies with plant species but is usually from 2 to 10 mol m-3 s-1. We can also estimate Vmax from measurements of the maximum rates of CO2 fixation by isolated chloroplasts. These maximum rates—which are sustained for short periods and are for optimal conditions—can be 100 mmol of CO2 fixed (kg chlorophyll)-1 s-1 [360 pmol (mg chlorophyll)-1 hour-1 in another common unit], which is approximately 3 mol m-3 s-1 (1 kg chlorophyll is contained in about 0.035 m3 of chloroplasts in vivo). In vitro, the key enzyme for CO2 fixation, ribulose-l,5-bisphosphate carboxylase/oxygenase, can have rates equivalent to 200 mmol (kg chlorophyll)-1 s-1. The estimates of Vmax using isolated chloroplasts or enzymes usually are somewhat lower than its values determined for a leaf Measurements using leaves generally indicate that KqOz is 5 to 20 mmol m-3. For instance, Kcch can be 9 mmol m-3 at 25°C with a Q10 of 1.8 (Woodrow and Berry, 1988 Q10 is defined in Chapter 3, Section 3.3B). 

While the value for Q10 of chemical and enzyme-catalysed reactions lies in a narrow range (between 2 and 3), values for disinfectants vary widely, e.g. 4... 

Q10 Which of the following 1.00 mol aqueous solutions would have the highest pH value ... 

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