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The Effects of Various pH and Temperature on the Enzyme Activity of Phytase - Biology

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The Effects of Various pH and Temperature on the Enzyme Activity of Phytase - Biology

Abstract Background: Phytases (myo-inositol hexakisphosphate phosphohydrolases) catalyse the release of phosphate from phytic acid myo-inositol hexakisphosphate (InsP6) and is the major phosphorus-storage form in plants, including most cereals and legumes. Methodology/Principal Findings: The influences of pH on phosphatase activity on wheat phytase were investigated. Para-nitrophenyl phosphate (pNPP) was used as substrate .This allows more varied experimental procedure to be conducted as InsP6 is readily precipitated by many metals and other conditions. Using pNPP, we are able to determine the effect on the enzyme. Citric acid (0.1M) and trisodium citrate (0.1M) allowed us to select a range of pH values (3 – 6) at which phytase activity could be tested. A calibration curve was prepared using a standard p-nitrophenol. Conclusions/Significance: The pH optimum for phytase, using pNPP as substrate was pH 6. The activity rapidly fell away (Vmax 0.048 + 0.002moles/min at pH 6, 0.0075 + 0.0003moles/min at pH 3. Changing the pH did not affect the Km.  
  1. Introduction

During the last 20  years, phytases  involved substantial  courtesy  from  both  experts  and  analysts  in  the  areas of gaining a particular rationale over this subject that further leads towards the aspects of the environmental protection aspects and concerns of the biotechnology.  These  enzymes  fit  to  a  singular  aspect of class concerning  the phosphomonoesterases  (myo-inositol  hexakisphosphate  3-phosphorylase,  myo-inositol  hexakisphosphate  6-phosphorylase,  EC  ,  and  are  accomplished  of  introducing  the  main release  of  phosphate  from  phytate  [myo-inositol  hexakisphosphate],  which  is  measured  the  main storage procedure of phosphate  in  the aspects of enzyme activity  (De Angelis, 2003). Phytases  were  first  planned  as  an  animal antibacterial feed stuff to improve the nutritious quality of feedstuff for simple-stomached faunae by redemptive phosphate (Moss, 1997).More lately, adding of phytase has been  understood as a  method to decrease the main constituents of  phosphate pollution in areas of concentrated animal  manufacture.  Numerous  lessons  have  exposed  the  efficiency  of  additional  bacterial  phytases  in  refining  use of phosphate from phytate.  Therefore, inorganic phosphate supplementation can be utilized in the aspects of the foods for faunae can be removed by counting various quantities of phytase and as an outcome, the phosphate excretion of these faunae may be condensed to the concentration of by almost 50% (Kerovuo, 1998).  Because of these particular findings that it could be used to protect the animal fee stuff , researchers started to use phytate as an anti-nutrient by combining it with the proportions of proteins and by mixing it with proper minerals, a biotechnological concern of phytase in the aspects of food area can be visualized also, this particular information and usage let us to investigate that what could be the effect the influence of temperature and pH (3-6) on the prospects of enzyme specifically from pNPP substrate to pNP metabolism by wheat phytase (Rousseau, 2012). 

The  act  of  phytase  also  donates  towards  plummeting the contamination in diverse superficial and ground water produced by the phytate  and  phosphorus  run-off  from  dung  in concentrated livestock districts (Hayes, et al., 1999). All the market obtainable phytases are histidine acid phytases with best doings at low pH and with low thermo stabilities (Igbasan, 2000). Alkaline phytases happens to be definitively recognized as β-propeller phytases,  are lively at unbiased or somewhat alkaline circumstances, calcium-dependent, and  are  fairly  thermostable  so  as  to  endure  the  critical temperatures  throughout  the  pelleting  of  bodily feeds.  They can henceforth exhibition doings in the minor intestine of faunae as well as throughout storing of diverse market available stuff. (Ullah, 1988). Then, we deliberate the enhancment of physiological limits for phytase manufacture. After average enhancement, the enzyme cleansing steps were completed with the assistance of numerous chromatographic methods using an automatic ÄKTA Prime Plus scheme (Fruhwirth, et al., 2003). Some  preceding  educations  on  phytase  used  ion-exchange chromatographic methods as purification approaches while other  researchers utilized  gel  percolation  as  a  cleansing  method  for  phytase from  dissimilar  sources  (Choi, et al., 2001). The possessions of the pure enzyme were branded and the kinetic limits. Also, the consequence of immobilized bacterial cells on the manufacture of phytase was assessed (Selle, 2000).

The Arrhenius model improvised a conceivable reserve for demonstrating temperature when it is practical to the three rates complicated in the procedure: the substrate alteration rate and the enzyme denaturation rate at high and particularly low temperatures. This method was utilized to label the metabolism of poikilotherm animals in which the preventive influence of the rate is distinct by only one particular enzyme .The reckoning obtained was later rehabilitated by (Schoolfield, et al., 1981) who introduced an orientation rate at a pre-established temperature and particularly elaborated the restrictions in instruction to decrease the association amongst them. In vindictiveness of the official  foundation of this last method, the empirical reckoning future by dissimilar authors and altered by Zwietering et al.generated the best fits (with only the aspects of four particular strictures) when numerous exact models for measuring the result of temperature on the microbial development of Lactobacillus plantarumon a conservative philosophy medium MRS were associated.

 

 

 

  1. Materials and methods

Table 1.0

The table shows required amount of citric and trisodium citrate for each pH solution.

Sodium citrate buffer solution for pH 3.0-6.0

pH

ml 0.1M citric acid

ml 0.1M trisodium citrate

3

41

9

4

29.5

20.5

5

17.5

32.5

6

5.75

44.25

 

 

 

 

 

 

 

2.1.Materials

The materials utilized as a part of this research were wheat phytase (P1259) as an enzyme, para-nitrophenol phosphate (pNPP), para-nitrophenol (pNP), citric acid and trisodium. All these materials were obtained from Sigma Aldrich or Fisher UK by Dr. Safrany.

2.2.Assay for pHs

In order to prepare a solution for different pH, a quantity sodium citrate buffer solution was prepared. Citric acids (0.1M, 9.6g) were dissolved in 500ml distilled water in a conical flask. In a separate conical flask, trisodium citrate (0.1M, 14.7g) was prepared and dissolved in 500ml in conical flask. These were combined together in accordance of pH required. For pH 6, a combination of citric acid 5.75ml and 44.25ml of trisodium citrate was added together respectively. Similarly, pH 5 was 17.5ml of citric acid plus 32.5ml of trisodium. In pH 4, it was a 29.5ml of citric acid and 20.5ml of trisodium. Finally for pH 3, 41ml of citric acid was combined together with 9ml of trisodium citrate. The amount of solution required for each pH can be seen on table one which was provided by Sigma Aldrich. 

 

 

 

 

Table one- Sodium Citrate Buffer Solutions, pH 6.0 – 3.0

pH

X ml 0.1M citric Acid

Y ml 0.1 Trisodium Citrate

Total solution (ml)

pH 6

5.75

44.25

50

pH 5

17.5

32.5

50

pH 4

29.5

20.5

50

pH 3

41

9

50

 

 

 

 

 

2.3.Calibration

An amount of pNP required was weighted in order to prepare for 16mM solution for calibration curve. A set of 5ml of twelve test tubes obtained and labelled with different concentrations ranging from 8mM, 4mM, 2mM, 1mM, 0.5mM, 0.25mM, 0.125mM, 0.0625mM, 0.0313mM, 0.0156mM, 0.0078mM and Zero containing only buffer. All twelve test tubes received 1.2m buffer. A 1.2ml of the 16mM pNP solution was taken from  and added to the 8mM test tube and series dilution were followed by pipetting 1.2ml of a previous higher concentration starting from 8mM, 4mM, 2mM, 1mM, 0.5mM, 0.25mM, 0.125mM, 0.0625mM, 0.0313mM, 0.0156mM, 0.0078mM and Zero.

The solution in test tube labelled as a zero was transferred into cuvette and used to set spectrophotometer as a reference at 405nm.  A spectrophotometer was used to read absorbance of the rest of the concentrations of the pNP solution starting from 0.0078mM up to the 8mM content. The result was typed on software called Prism Graph to calculate the amount pNP present in control set and non-control at 0min, 15min and 30min. 

In order to calculate the amount of pNP present in standard curve, the result was typed up on software called Prism Graph. The data was analysed and interpolated as standard curve where hyperbola is the concentration. This was repeated three times for each pH experiment and the best result was taken.

2.4.Assay

The standard assay utilised to determine the effect of wheat phytase and this was performed according to the protocol of the experiment. Rates of PNP formation were calculated using the standard curve. Two set of ten test tubes obtained and labelled with different concentration. 0.125mM, 0.25mM, 0.5mM, 1mM, 2mM, 4mM, 8mM, 16mM, 32mM, 64mM. One set contained phytase and the control had no phytase in it. The phytase 0.2mg/ml (0.3ml) was incubated at 370C with 0.6ml pNPP concentrations and volume of 0.3ml of pH. The total volume of solution mixture was 1.2ml. A 128mM concentration of pNPP solution was prepared and diluted to make up 64mM. This was then serial diluted to make the concentrations 32mM, 16mM, 8mM, 4mM, 2mM, 1mM, 0.5mM, 0.25mM and 0.125mM.

One ml In control set was pipetted from each test tube containing the following concentrations 64mM, 32mM, 16mM, 8mM, 4mM, 2mM, 1mM, 0.5mM, 0.25mM and 0.125mM and placed into one ml cuvette which was transferred into spectrophotometer 405nm. In non-control set, the enzyme phytase was added at 0min, 15min and 30min and at the same time the absorbance reading taken. This was repeated three times at each concentration the best result was taken out of the three results. This was done for both control and non-control set.

In order to calculate the amount of pNP present in each test tube at particular time, The result was typed on software called Prism Graph. First standard curve was prepared as mention under calibration. The result from control set and non-control at 0min, 15min and 30min was typed in new data in prism graph.  The data was analysed in linear regression and 0min in non-control set was then deducted from 0min in control set. This was done same way for 15min, 30min and the result was typed on new data sheet on Prism Graph. Data was analysed in non- linear regression and Michaelis Menten equation was used to produce Km and Vmax. This was repeated three times for each pH experiment and best result was taken out of the three results.

2.5.Determination of Km and Vmax for the hydrolysis of phytase for pNPP.

Substrate of pNPP will be added into all tubes then enzyme or enzyme will be added to each particular tube one at a time, these will be transferred into a cuvette, a particular absorbance reading and the remaining contents will then be added to another tube. Raise at 37oC between interpretations. Particular readings will be taken at the intervals of the 0, 20, 40 and 60 minutes after the totalling of enzyme or enzyme. The cuvette will be reprocessed then, and stirred well to discourage cross-contamination.

128mM pNPP will be utilized and dilutions of 2-fold serial will be made (the top concentration that would be needed is 128mM, as when its particularly diluted 1:1 with enzyme comprising phytase the concluding concentration will be 64mM), as you have complete for the normal curve. 0.6ml will be utilized for two conditions at each substrate solution. 0.6ml enzyme will be added or 0.08mg/ml phytase to the aspects of the each tube. By utilisation of a stop-watch you can add enzyme or enzyme to particular tube with a minute delay among additions. These aspects would allow to take reading at all levels

As the concentration of substrate increases, the degree of metabolism also tends to increase. This particular relation association is not linear as it is directly proportional, and this reaction stops at higher substrate concentration

Vmax is the maximum velocity the reaction can avail at lower concentration of substrate. It can never be calculated accurately but a somewhat near value could be accumulated, on the other hand as our rectangular hyperbola methods this level an approximation can be resolute. That would renter this at a later time and reflects convinced linear alterations utilize an estimation of Vmax.

Km, the Michaelis constant, is elaborated as the proportion of substrate at which the velocity of a reaction is half the Vmax.

The Assay that would be determined in this particular study will show the aspects of the influence concerning to pH (3-6) and temperature on enzyme pNPP substrate to pNP metabolism.

Particular substrate concentration has been used to obtain a normal curve while Phytase (0.16mg/ml, 0.2ml) has also been included in the experiment with 0.6mM pNPP, in the attendance of increasing proportions of divalent cations at  volume of 0.3ml. The total volume of the assay can be initialized as 1.2ml. Assays were achieved at 37oC in a MOPS comprising buffer at pH 6.0-3.0 with absorbance standards taken after the intervals of 0,15,30 minutes at the aspects of wavelength of 405nm. No enzyme was utilized for the normal control for pH (6-3) and temperature. Control tubes were also utilized to conduct this experiment and check the effect of the pH (6-3) and temperature on enzyme.

 

  1. Results

The wheat phytase catalysed the breakdown of pNPP to pNP. The rate of hydrolysis was monitored over the time of 0min, 15min and 30min for different pHs.  At pH 6, phytase caused breakdown of pNPP to pNP with a classical Michaelis Menten profile graph was produced. Increasing the substrate concentration increased the rate of hydrolysis. As the concentration of pNPP exceeded 10mM, the rate continued to increase, but the rate of increase declined. Analysis of these data identified a Vmax and Km of 0.04886 µmol/min/mg and 6.991mM on figure one. The enzyme developed its saturation with substrate pNPP. Furthermore, when the catalytic site gets empty, more pNPP substrate is obtainable to dissolve and undergo the reaction. The rate of particular formation of the needed product that is p-nitrophenol + phosphate,  is now depending upon the particular activity of the enzyme itself, and the addition of more substrate will not be needed to influence on effect the reaction to produce more changes

Vmax and Km results from different pHs

pH

Best-fit values Vmax

Best-fit values Km

Std. Error Vmax

Std. Error Km

R square

6

0.04886

6.991

0.002172

1.001

0.9880

5

0.03581

7.762

0.001814

1.235

0.9850

4

0.009233

0.4032

0.0007342

0.1720

0.7975

3

0.007482

4.899

0.0003195

0.7310

0.9841

 

  1. 1.      Discussion         

Particular factors that influence the enzymatic assessment

The Michaelis-Menten equation is mainly utilized to view the aspects that concern with the kinetics of reaction catalysis by enzymes. Typically, reaction velocity that is also called as the rate of reaction against different substrate concentration  (Cano, et al., 2013).. This particular range of reaction of substrate concentrations is used in particular way so that precise values can be recorded. A particular plot of the reaction rate versus the substrate concentration would be able to signify the two main vital kinetic parameters: Vmax and Km.Vmax states the maximum reaction rate at different saturating values of the substrate concentration. Vmax is a function of the intrinsic rate of the enzyme or in other words it could be said that a particular transporter of the molecules. Km is called as the Michaelis constant and is related with the substrate concentration. Km is noted as inversely linked to the affinity of the enzyme transporter for its substrate. Consequently, Km value that is mainly lower refers to a very high aspect of affinity of collaboration between the enzyme and its substrate. This particular statement could be seen in the results that in no time the small concentration of substrate achieve the ½ value of Vmax. Contrariwise, a relatively high numerical value that concern with the aspects of Km is share the idea of a low affinity of the transporter for its particular substrate. This is due to the fact that it takes high concentration of the substrate to reach up to the half value of the saturating concentration. Thus, Km is a very valuable parameter by which the aspects of the affinity of the concern enzyme for various substrates can be associated  (Hendrickx, 1998).

It is needed in this particular research to highlight that the kinetics of transport for many particular enzymes exhibit the same features that are stated in the results section of this particular research. Furthermore it could also be realized that the transporters show their proper reaction according to different types of substrate and their concentration that could also can also be realized in the results section that not all enzymes exhibit the same reaction rate and specificity with the Km , Therefore, the kinetics of many transport procedures can be deliberate by utilization of the Michaelis-Menten kinetics. The Michaelis-Menten equation could easily be able to determine the enzyme activity and furthermore the relation between the Vmax and substrate concentration transporters.

. In many researches it can be seen that the activity is particularly calculated in the opposed direction to that of the direction concern with the enzyme’s usual function. Yet, with a whole revision of the parameters that influence the activity of enzyme that it should be conceivable to infer to the activity that is mainly predictable to be stirring

The influences that affect the activity of an enzyme comprise of the aspects of the substrate concentrations, pH, and temperature (Wolberg, 2004). The opening rate of substrate operation when no products are existent (Bowers & McComb., 2010). There are many mixtures that might perform as inhibitors which block the movement, so they must not be contemporary (Abuchowski, 2001). The topic of enzyme inhibitors is a multifaceted that is not relative to this particular research. Though, it is worth noticing that the opposite, specifically the participation of non-substrate enzyme relative activators, must be appeared to with several enzymes, meanwhile they can be completely sedentary without the presence of an activator (Schmaljohann, 2006).

 

1.1.The particular influence of substrate concentration

The customary enzyme possesses aspects that are concern with the insinuation of hyperbolic response to substrate concentration, rendering to the Michaelis–Menten equation that says;

 

Where [S] is the substrate concentration, v is the rate measured, Vmax concern with the aspects of maximum hypothetical rate at immeasurable substrate concentration, and Km is related to the Michaelis constant (Asgher, 2007). This formula is applied to find the result of v is one-half of V max when Km. the substrate concentration that are mainly utilized in enzyme assays is selected rendering to perspectives of such as the Km, the solubility of the substrate, whether great concentrations may constrain, and the charge of the substrate (Jiang, 2005). If standards are relatively less than 2 Km are utilized, then it happens to be more important to know precisely whether the concentration is (some preparations of rare substrates may be contaminated, or the particular amount present may not be recognized) (Green, et al., 2006). This is since the rate measured differs with substrate concentration more quickly as the substrate concentration reduces as shown in the aspects of the results that are shown earlier in this particular aspects of research (Yagiz, et al., 2007). In most of the aspects an enzyme assay has previously been recognized, and the particulars of substrate concentration, buffers and other aspects are utilized previously should be utilized again. There are many enzymes which are not able to signify the results on the basis of the Michaelis–Menten formula (Sinsabaugh, 2008). With many aspects that are relative to the allosteric enzymes an activator is mainly used and this can change the sigmoid aspects into the shape of the hyperbolic curve  (Meng, 2003).

 

1.2.The particular effect of pH relative to the enzyme activity

Enzymes are mainly concern with the aspects of active only within a particular range that has been relative to the pH. But the restrictions could be different it could vary from pH of 5 to 10, or narrow that could be of 1 pH per unit  (Yancey, 2005). Within the particular range there has to be the presence of an optimum at which the main and which is mostly called as the maximum activity (the highest value for Vmax) is reached: there is a possibility of a particular short range in itself (Yang & Pan., 2005). The activity can also be pretentious by the aspects of the nature of the buffer used. There could be a concern of some particular discontinuity in the aspects concern with the particular activity over the pH range verified since of the utilization of dissimilar buffers (Klompong, 2007). Substitute buffers for an assumed pH always have to be tested. The particular effect of pH is usually tested at the aspects that are concern with the insinuation of particularly high substrate concentration (Baş & Boyacı., 2007). However, if it is tested at the aspects of the low concentration, then it is a possible scenario that the value of v would be able to vary with aspects that are concern with the insinuation of pH because of an influence that was not imposed to V max, but on Km. For normal enzyme assays, a particular value of pH is mostly chosen that is near to the aspects that are concern with prospects of the optimum, unless some other constituent of the assay mixture would not be able to function at that pH (Damar & Balaban., 2006).

It should be renowned that the optimum pH concern with prospects of reaction direction-specific. In most of the situations, the optima in the aspects that are concern with prospects of two directions will be dissimilar, particularly if there is acceptance/ evolution of a proton in the reaction (Gao, 2008).

1.3.Effect of temperature

Temperature influences enzyme activity in a particular and similar way, as it happens to impose an influence on the aspects that are concern with prospects of other chemical reactions (Palmieri, et al., 2005). Rates upsurge by amid 4 and 8% per degree C, though at the aspects that is concern with prospects of high temperatures denaturation of the enzyme protein reduces the concerns of the product formation (Patras, 2010). Thus it is imperative when carrying out the particular aspects of the enzyme assay to guarantee that the temperature should be kept constant at a particular rate throughout the particular experiment and this particular temperature should be noted and known (Rodrigues, 2013). For contrast with other particular results that may have been stated at other particular aspects of temperatures, the precise temperature coefficient should be recognized; if it would not be, a figure of  % per degree happens to be utilized as approximation (Shah, et al., 2005).

1.4.Measurement of Enzyme Activity

Stopped assays

To measure the aspects concern with the activity of an enzyme one must calculate how much product is produced over a particular amount of time or, in some prospective, what is the quantity of substrate that is used, which the same as the other aspects is discussed above (Lee, 2008). Thus preferably a technique for calculating whichever product or substrate in the attendance of the other is obligatory. There are numerous dissimilar methods; this dissuasion will deal with the aspects that are concern with prospects of ‘stopped assays’ (Rhee, 2005). Stopped assays comprise stopping the reaction after a fixed interval of time, then assessing how much product has been shaped. Any method is likely, from chemical, enzymatic to bioassay, and usually the simplest is selected provided it is dependable (Pandya, 2005).

In many particular aspects a relatively selective method can differentiate among substrate and product, so that no parting step is compulsory (Merino & Cherry., 2007). For instance, phosphate issue from a phosphate ester can be calculated by the typical phosphomolybdate process. Then separation of unused substrate from the aspects that are concern with prospects of product may be wanted. This is indispensable with radiochemical assays, in which the calculation is of radioactivity, not a exact test for the product itself (Asad, 2007).

Separation methods comprise chromatographic and the aspects that are concern with prospects of thin-layer chromatography, TLC; high-performance liquid chromatography, HPLC), it also includes solubility and partition measures (Lee, 2006). Approaches for discontinuing the reaction comprise those which denature the enzyme, such as the aspects that are concern with prospects of strong acid, alkali or detergent; heat; or treatments with the aspects that are concern with prospects of irreversible inhibitors such as the instance heavy metal ions. In some cases the enzyme can be immobile by adding of a complex agent that could be of ethylene diaminetetraacetic acid (EDTA), which eliminates metal ions vital for activity; even chilling on ice may be adequate (Huff-Lonergan & Lonergan., 2005).It is significant that stopped assays are checkered at least once with variable times of incubation, to safeguard that the rate is same through the interval designated for the standard technique (Saha, 2005).

  1. Conclusion

It could be concluded that the rate of velocity increases as the substrate concentration increases but it could be observed in these particular cases that enzymes have been saturated with different amount of substrate concentration. In some enzyme the substrate concentration tend to achieve the ½ Vmax quickly while in others it was unable to achieve the ½ Vmax value at the same rate. Additionally, the reaction rate depends on particular properties of the enzyme (K, kcat) and the aspect concern with the enzyme concentration (E).

  1. Recommendation

According to Liu et al., (1998), the optimum temperature for Phytase is around 45-60C. The temperature for this experiment was 37°C; therefore, the enzyme may have not reached an optimum temperature for it to be effective. In future, it will be appropriate for the wheat Phytase to be put away and must take care of it in according to the manufactures recommendation.

Individual spectrophotometers were utilised as a part of reading the absorbance of the product. It was examined that some of the spectrophotometers gave low readings; there were others which gave high readings. The spectrophotometers were used by different students who used for different experiment and transferred from one laboratory to another. This may have had some impact on the outcomes. In future, the project student should have their own spectrophotometers duration of their practical to minimize errors of the experiment.

It has been recognised that phosphate acts allosterically to inhibit Phytase non-intensely; notwithstanding, there is scarcity of data out there to bolster this perception. It will be vital for somebody to repeat these analyses with the focuses utilised and to create the instrument by which phosphate works and a pattern

 

 


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