Introduction
In addition to their important roles in natural environ-
ments, microbial enzymes can be highly specific in their
activity and thus are increasingly useful in industrial
applications. Enzymes from aquatic bacteria adapted to
moderate and high temperatures have already figured in a
variety of applications, including polymerase chain reac-
tion (PCR), laundry detergents, protein recovery and
organic synthesis (e.g. Mullis and Faloona, 1987; Adams
and Kelly, 1995). Although enzymes with optimal activity
at cold temperatures have been understudied compared
with their heat-stable counterparts, increasing attention is
being paid to cold-active enzymes as potential applica-
tions are revealed
Enzymes are the principle molecules that work in the cell. They can build, split and reorganize the molecules of life (Starr, 2005). The activity of an enzyme may be affected by some factors, particularly environmental one, such as temperature (Campbell, 1996). The way enzymes respond to temperature is fundamental to many areas of biology (Daniel, et al., 2010).
Each enzyme has conditions under which it works optimally because they have an influence in its conformational structure. So, each type of enzyme has an optimal temperature at which the reaction is fastest, meaning that it has a slower reaction at other temperatures. The optimal temperature of reaction allows for the greatest number of molecular collisions without denaturing the enzyme (Campbell, 1996). This influence of temperature on the modification of proteins makes this parameter a robust selective force on the evolution of this macronutrient (Lockwood and Somero, 2012)
Most human enzymes’ optimal temperature is between 35ºC to 40 ºC. One of these enzymes is the Lactate dehydrogenase, which catalyzes the conversion of lactate to pyruvate (Figure 1). This step provides energy to the cell, especially in some organs, such as the heart, kidney, and muscle. Lactate dehydrogenase A (LDH-A) is a NADH-dependent enzyme (Fan, et al., 2011). When co-enzyme (NADH) is reduced, it can absorb light at a wavelength of 340 nm, but not when it is oxidized (NAD+); this provides an easy way to measure the reaction (Vanderlinde, 1985).
Figure 1. Conversion of lactate to pyruvate with the activity of the lactate dehydrogenase. (https://www.google.co.ve/search?q=lactate+dehydrogenase+reaction+lactate+to+pyruvate&safe=off&espv=2&biw=1366&bih=667&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj-isiUvs3KAhWG7SYKHbJ6AJ0QsAQILA#imgrc=MZKbRDX9Bv6Y1M%3A)
Lactate dehydrogenase is the most clinically important of several dehydrogenases occurring in human serum (Vanderlinde, 1985).
The aims of this research were to establish a method to determine the initial rate of reaction for an enzyme; to observe the effect of different temperatures on the rate of the enzyme activity; and to explain why those different temperatures can cause various effects on the enzyme.
Method
Three different experiments were performed in order to determine the effect of the temperature on enzyme activity. Three mixes of 1.9 mL of NAD+ solution, 1.0 mL of lactate solution, and 100 µl of the enzyme were prepared. In the first experiment, all components were used at 21 ºC. In the second, the lactate solution were used at 37 ºC and the other components at 21 ºC. Last, in the third one, the enzymes were incubated at 65 ºC.
All components stood for 15 minutes at the established temperature. After, the mixes were prepared, and the absorbance (340 nm) was read every 10 seconds.
Results
Different results were found at the different treatments. Table 1 shows the minimum, maximum, mean and the initial rate reaction for the three experiments. The highest absorbance value was observed on Experiment 1 (0.172).
The initial rate was calculated using the tangent of the curve, as shown is Fig. 2. The initial (maximal) rate of reaction was from 0.027 to 0.003 ΔA340/min, being the highest one at 21 ºC (Fig.3).
Discussion
Enzymatic activity is influenced by the temperature. When the enzyme and the substrate come into contact with one another, the reaction starts. This process can be measured spectrophotometrically through the measure of the NADH, as it produces the enzymatically active NAD+ (Chan and Bielsky, 1974).
The velocity of enzyme reaction is related to the temperature, as well. An increase of the velocity is evident when temperature increases because the substrate collides with active sites more frequently when the molecule moves rapidly, and this occur when temperature increases. (Campbell, 1996).
However, this process can be stopped at some point of the temperature scale because the high thermal agitation of the enzyme molecule disturbs the interactions of the active conformation. This disruption of the enzyme and substrate produces the protein denaturalization. (Campbell, 1996). This phenomenon could have happened at 65 ºC, where the absorbance of the NADH is the lowest, which demonstrates that the enzyme activity was too low. It is also evident by the initial rate reaction with a value of 0.003 ΔA340/min. Elias et al, 2014 reported a > 10-fold less enzymatic activity per 25ºC increase in temperature.
An intermediate inactive (but not denatured) form has been proposed between the enzyme activity increased by the temperature and the denaturation of the enzyme. This form is in rapid equilibrium with the enzyme active form. (Daniel, et al., 2010).
The initial rate (maximal) reaction showed that the highest maximal product formed per time was at 21 ºC (0,027 per minute), which corresponds to the best temperature for the enzymatic reaction. Elias et al, 2014 reported a rate-temperature dependency of the thermophilic, mesophilic and psychrophilic enzymes, showing a similar pattern of dependence. Daniel, et al., documented a low temperature (15 ºC) as optimal, at sea-ice samples.
Conclusions
The highest enzymatic activity was shown at 21 ºC with more than a 99% increase in enzymatic activity with respect to 65 ºC.
Similar results were found between the activity at 21ºC and 37 ºC.
An experiment working at 45 ºC or 50 ºC can be useful to see the difference between 37 ºC and 65 ºC range.
References
Campbell, N., 1996. Biology. California: The Benjamin/Cummings Publishing Company, Inc.
Chan, P.C., Bielski, H.J., 1974. Enzyme- catalyzed free radical reactions with nicotinamide adenine nucleotides ii. lactate dehydrogenase-catalyzed oxidation of reduced nicotinamide adenine dinucleotide by superoxide radicals generated by xanthine oxidase. The Journal of Biological Chemistry, 249, pp, 1317-1319.
Daniel, R.M., Danson, M.J., Eisenthal, R., Lee, C.K., Peterson, M.E., 2007. The effect of temperature on enzyme activity: new insights and their applications. Extremophiles, 12(1), pp.51-59.
Daniel, R.M., Peterson, M.E., Danson, M.J., Price N.C., Kelly, S.M., Monk, C.R., Weinberg, C.S., Oudshoorn, M.L., Lee, C.K., 2010. The molecular basis of the effect of temperature on enzyme activity. Biochemical Journal, 425(2), pp.353-360.
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Huston, A.L., Krieger-Brockett, B.B., Deming, J.W., 2000. Remarkably low temperature optima for extracellular enzyme activity from artic bacteria and sea ice. Environmental Microbiology, 2(4), pp. 383-38.
Lockwood, B.L., Somero, G.N., 2012. Functional Determinants of Temperature Adaptation in Enzymes of Cold- versus Warm-Adapted Mussels (Genus Mytilus). Molecular Biology Evolution, 29(10), pp. 3061-3070.
Starr, C., 2005. Biology Today and Tomorrow. Belmont: Thomson Brooks/Cole.
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