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Urease is the enzyme that converts urea into ammonia and carbon dioxide, bzw. into ammonium and carbonate ions (sometimes also hydrogen carbonate ions).
Urease belongs to the group of ammidases and is commonly found in plant seeds, bacteria and crabs and sea shells. Plant urease acts independently of the urea cleavage mechanism as an insecticide and causes aggregation of platelets in mammalian blood.
Indeed, urease in soil bacteria in particular plays an important role in the nitrogen cycle. Without them, nitrogen fertilization would be possible because of decomposition in the absence of enzymes. Resistant urea, a component of manure, is not possible. On the other side are the Urease - positive bacteria in manure, the CAUSE of unwanted ammonia Emissions in animal husbandry. In Germany an estimated 490,000 of the 590,000 tons of total ammonia emissions!
The catalytic activity of the enzyme increases the reaction rate by a factor of 10 to the power of 14!
Importance for agriculture
Urease in soil bacteria is a prerequisite for the action of excreta Nitrogen fertilizer, because only the hydrolytic cleavage of urea yields nitrogen as ammonium Makes ions available to plants! However, the intermediate product, ammonia, is gaseous and contains only small amounts of gas can be absorbed by soil moisture. Some of it always escapes Ammonia is lost as fertilizer. This proportion is greater the more concentrated The raw material urea is present and therefore most ammonia is lost from barn floors and manure.
Because ammonia is also damaging to the environment in several ways and is internationally known After agreeing to reduce emissions, one of the efforts is to solve the problem using urease inhibitors - substances that limit or prevent the action of the enzyme - and reduce Co2 equivalent emissions from livestock production.
Nitrogen loss after fertilization
Urea is the most commonly used nitrogen fertilizer. In normal use as As a component of fertilizer, the applied urea is broken down by the urease activity ofBottom bacteria into ammonia and carbon dioxide, some of which escapes through the air, This means that 15 to 35% of the nitrogen in the soil is lost! This cannot be reduced by adding Urease inhibitors. At the same time they slow down the availability of nitrogen so overnitrification cannot occur!
Ammonia emission from farmyard manure
Ammonia is harmful to the environment in several ways and there are agreements about Emission Limits. Because about 80% of ammonia emissions come from agricultural operations, there is potential use of urease inhibitors. This is more promising than fertilization because barn conditions can be better controlled. Emission reductions of 50% have already been achieved in tests.
Urease Inhibitors
Urease inhibitors are chemical compounds that reduce or completely prevent urease activity. Chemically, they include phosphodiamides, phosphazenes and thiols on derivatives of hydroxamic acid and urea. Application areas are in agriculture, medicine and basic research on the mechanism of inhibition. Heavy metal ions (mostly silver, mercury, copper and potassium azide) also inhibit urease. They cannot be used because of their toxicity! The use of ammonium thiosulfate fails because it depends on soil properties.
The effect of calcium ions and alkalis on the enzyme activity the urease
A detailed analysis of urease activity in animal husbandry can be found in the thesis of Martin Leinker - from the Institute of Agricultural and Food Sciences - University of Halle. Topic: Development of a basic solution to reduce ammonia emissions from livestock housing using urease inhibitors
Quote from the work:
“For the area of stable holding, it appears that urease is very stable against heat and the pH values of urine, feces and floor surfaces are optimal when they are around Ph 6 to 8. Liquid manure stored for long periods of time usually has a reducing effect on urease activity in the manure. The rougher and therefore coarser and uneven a surface is, the better In these places urease-producing microorganisms can settle. The dirtier they are stable surface, the greater the chance of high urease activity and thus urea splitting potential, on the barn floor!”
Quote page 83:
“The initial pH value of the surface of brand new floor coverings at the beginning of the test showed different levels depending on the material. While rubber floors and poured asphalt had Ph values of 8.7 and 8.5, respectively, a pH of 11.2 was measured on concrete floors, which is highly alkaline. From the 2nd day of the experiment (after contamination with feces and urea), all soil materials then had an average pH value of 9.5 - 9.3 - 9.2 in descending order from concrete, rubber and cast asphalt to substrate. Excreta and urea solution had mean pH values of 6.7 and 7.8. The pH values between 9.2 and 9.5 were thus in line with ammonia Release a favorable alkaline range. This increase in surface pH could be due to the increased effect of the urea hydrolysis reaction.
p pages 182 - 185 contains a treatise on pH in the liquid phase of manure. Also discussed is the ammonia balance, which occurs at higher pH values the emission of ammonia gas is increased. This is also understandable because yes Higher Ph values reach the saturation level of NH4+ ions and prevent further dissolution of ammonia.
Quote pages 150 - 151:
An influence of inhibitor application on surface pH could not be determined. The surface pH values of inhibitor-treated test plots differed significantly from untreated test plots. Overall, urease activity in the test plots increased significantly throughout the test period from about 1476 to a level of 466 mg NH4+ - Nm-2h-1 (-68%).
Proprietary analysis
The thesis relates to the inhibition of urease activity by inhibitors Urea storage in the enzyme and thereby hinder the cleavage of urea into CO2 and NH3. (Competing reactions with urea or change in steric alignment of the enzyme and blocking the active center around the nickel cation). Another and more effective option for inhibition is to intervene in the ammonia Equilibrium by shifting the balance.
Urease activity in terms of the Ph value has been sufficiently studied and replicated in experiments at universities and schools. The result is clear. The urease develops its best activity at a pH around 7! Because the splitting of urea produces ammonia gas, which dissolves only to a limited extent in water and ash Base can increase the Ph value to 11, only a limited amount of ammonia can be formed. Thus, the rate depends on the amount of ammonia gas diffusing into the air, releasing the further cleavage of urea. This process takes place at Ph 9 - 10 increases so that, as correctly described in the thesis, the Ph value at the surface remains constant. Higher PH values lead to a decrease in the reaction rate!
The Ph value of about 9.3 is explained by the maximum concentration of NH3 and NH4+ particles in chemical equilibrium (buffer region). At higher Ph values the ammonia content decreases again. The possibility of reducing the reaction rate by shifting the ammonia equilibrium to the left by adding alkalis was not considered in the thesis. But the concentration of hydroxide ions is affected by other alkalis Reagents increase, the proportion of NH4+ ions in solution decreases and thus the Solubility of ammonia. At the same time, the reaction rate and thus the escape of ammonia gas decreases! The added ions therefore change the steric alignment of the urease, leading to a blocking of the active center, after which optimal inhibition is achieved. This is the basis of a practical study we have conducted.
When solids, which form alkalis in aqueous solution with a pH of 11 - 12, are added to liquid manure with the known ratios of urine and water, the enzyme cannot initiate any or only a small amount of urea cleavage because its activity is too restricted. It is released only when the pH is lowered by diluting the solution with water - for example, in the field by rain! These solids - e.g. slaked lime forcing a pH of >12 - have exactly that Effect sought as inhibitors in agriculture.
Double positively charged cations such as Ca2+ or Mg2+ ions can change the tertiary structure of the enzymes when the concentration is sufficient. That is, adapt to the proteins to add that intermolecular bonding occurs via hydrogen bonds or Van der Waal's troops are disrupted. This process is reversible, meaning that if the reaction environment changes, the enzyme can become active again.
The impact of our product is on this action, even in the manure on the barn floor. The otherwise stench in the animal houses decreases significantly, but so do the manure basements. At the same time, the consistency of the manure becomes more fluid. In addition, the additives in the product ensure that the moisture in the barn floor is absorbed The absorption of water is reduced and the activity in the aqueous solution is again restricted.
The inhibitory effect can be reversed by increasing water intake. Because some of the easily soluble leach is washed out of the manure by rain. This means that the urease can regain its activity after it is applied to the field, allowing Nitrogen fertilization of the soil.
The influence of pH values higher than 10 on the ability of bacteria to produce urease has not yet been studied. However, experiments have shown that this is clearly limitation occurs.