Urease inhibitors are specialized substances used to reduce urease activity. It can inhibit the activity of microbial urease in the rumen of ruminants, slow down the decomposition rate of urea, and make the rumen microorganisms have a balanced supply of ammonia nitrogen, thereby improving the utilization rate of urea by ruminants. The substances that can be used as urease inhibitors generally have the following types:
1. Acetohydroxamic acid (abbreviated AHA) is a white or pale yellow crystalline material obtained by chemical synthesis. The melting point is 88 to 92 °C.The aqueous solution is slightly acidic. It is easy to absorb moisture, and it is easy to change color when exposed to light. It is easily soluble in water, ethanol, ether and the like. Acetylhydroxamic acid (AHA) is a very effective urease inhibitor. It can inhibit rumen microbial urease activity in ruminants, regulate rumen microbial metabolism, increase microbial protein synthesis (25%) and cellulose digestibility, and reduce urea decomposition rate in rumen.
2. Hydroquinone (HQ), also known as hydroquinone. The molecular weight is 10.10. It is a white crystal. The boiling point is 286.2 °C. It is soluble in water and is compatible with alcohol in any proportion. Its role is mainly to inhibit the activity of urease in the soil.
3.Benzoquinone, molecular weight 108.10. This product is yellow crystal; it has a special smell and can sublimate. It dissolves in ethanol or ether and is slightly soluble in water.
4. Sodium tetraborate (Na2B4O7•10H2O), also known as borax, is a colorless translucent crystal or a white monoclinic crystalline powder. It is odorless and salty. The relative density is 1.73. Crystal water is lost at 60 ° C, and all crystal water is lost at 350-400 ° C. It is easily soluble in water, glycerin, slightly soluble in alcohol, and the aqueous solution is weakly alkaline.
5. Heavy metal salts generally include heavy metal ions such as Mn2+, Ba2+, Co2+, Cu2+, and Fe2+. Among them, Mn2+ and Ba2+ have the best effects, but these ions also inhibit the activity of other enzymes.
Mechanism of action of urease inhibitor The type of urease inhibitor is different, and the mechanism of inhibition of urease is also different. At present, hydroxamic acid compounds (especially acetohydroxamic acid) are considered to be the most effective inhibitors of urease (Mapadevan, 1976).
The name of acetohydroxamic acid is N-hydroxyacetamide, which has the formula CH3-CO-NHOH and a molecular weight of 75.05. There is a hydroxylamine structure (-NHOH) in the molecule of acetohydroxamic acid, and its active hydrogen and hydroxyl groups combine with the sulfhydryl group (-SH) of the adjacent metal nickel (Ni) in the urea structure to form a urease inhibitor-urease binary complex. As a result, the activity of urease was inhibited. The urease inhibitor does not bind to the binding group of the urease active center, but binds to the catalytic group of the urease active center, and inhibits the activity of the enzyme by changing the conformation of the urease.
It can be seen that the inhibitory effect of acetohydroxamic acid urease inhibitor on urease production is a reversible non-competitive inhibition. That is, the inhibitor does not affect the binding of urease to the substrate (urea), does not change the Michaelis constant (Km) of the urease (ie, does not change the affinity of the enzyme to the substrate), but only reduces the reaction rate (V) of the urease-catalyzed substrate. This will ensure that urea (exogenous urea and endogenous urea) can still be hydrolyzed by urease in the rumen, slowly releasing ammonia to meet the nitrogen needs of rumen microbial proliferation.
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