Hydrolysis reaction, microbial

Table 17.3 Some Microbially Mediated Hydrolysis Reactions...

Plants. Three major metabolites have been identified, isopropyl water-soluble conjugates of glucose or other plant components Soil. Microbial degradation leads to the production of 3-chloroaniline by an enzymic hydrolysis reaction, with liberation of C02. DTJ0 in soil c. 65 days (15°C), 30 days (29°C)... 

Hydrolysis reactions of great variety commonly occur on microbial cell surfaces (Fig. 2.4). Phosphatases that degrade phosphomonoesters, urease that degrades urea, carbonic anhydrase that catalyzes the interconversion between bicarbonate and carbon dioxide, and proteases that attack amide bonds in proteins, to name a few, are present. Some of these enzymes are found inside as well as on the surfaces of cells. 

Unstable in alkaline media. Stable in acid and neutral media. Decomposes above 150°C. Most important metabolite is CO2, formed by microbiological degradation of the phenol compounds. ty2 (river water environmental conditions) 13.5 days (pH 7.5), and (pond water 26 to 30°C) 2.3 days (pH 7.8 to 8.5), and (deionized water 27 2°C) 36 days (pH 7), and (deionized water 27 2°C) 1.2 h (pH 10). ty2 (soil) 30 to 60 days Hydrolyzed slowly in acid and alkaline media. Stable to UV light. Decomposes above 150°C. In soil, microbial degradation yields 3-chloroaniline via an enzymatic hydrolysis reaction with release of CO2. ti/2 (distilled water)... 

Binding of the substrate urea to a nickel ion in urease is an integral part of the mechanism in the hydrolysis reaction (Nielsen 1984). Both ruminants and monogastric animals require urease for the decomposition of urea into ammonia, which is needed for the microbial synthesis of ammonia that, in turn, is necessary for amino acid and protein synthesis. This process also takes place in the appendix of monogastric animals and some species of ruminants (roe deer). 

Degradation and evaporation seem to be the major pathways for acrolein loss in water smaller amounts are lost through absorption and uptake by aquatic organisms and sediments. The half-time persistence of acrolein in freshwater is 38 h at pH 8.6, and 50 h at pH 6.6 degradation is more rapid when initial acrolein concentrations are less than 3000.0 pg/L. Acrolein has a half-time persistence of 2.9-11.3 h at initial nominal concentrations of 20.0 pg/L, and 27.1-27.8h at 101.0pg/L. At pH 5, acrolein reacts by reversible hydrolysis to produce an equilibrium mixture with 92% beta-hydroxypropionaldehyde and 8% acrolein in alkali, the primary reaction is consistent with a polycondensation reaction. Microbial degradation plays a major role in the ttans-formation of aaolein in aquatic systems. In natural waters, acrolein degradation proceeds to carboxylic acid via a microbial pathway beta-hydroxypropionaldehyde is readily biotransformed in about 17.4 days. 

In general, abiotic substitution reactions proceed slowly, but can be greatly accelerated by enzymes. Enzyme-mediated substitutions frequently involve cysteine residues in proteins or peptides, such as glutathione. Biotic and abiotic hydrolysis of halogenated aliphatic compounds yields alcohols by hydros l substitution at the halogenated carbon [10]. If these alcohols are themselves halogenated, further hydrolysis to acids or diols can occur. Examples of microbially-mediated hydrolysis reactions, together with responsible enzymes, are provided in Table 1. 

Photochemical degradation may cause changes in the monomer imit (by oxidation reactions), the macromolecular chain (through crossUnking or chain scission reactions), and even on the macroscopic scale [7, 25]. Thermal-oxidative degradation, hydrolysis and microbial attack are simultaneously promoted by the presence of the other associated factors (oxygen and ozone, temperature and freeze-thaw cycles, environmental moisture and microorganisms) and contribute to the overall effect [26-29]. 

Plasteins ate formed from soy protein hydrolysates with a variety of microbial proteases (149). Preferred conditions for hydrolysis and synthesis ate obtained with an enzyme-to-substrate ratio of 1 100, and a temperature of 37°C for 24—72 h. A substrate concentration of 30 wt %, 80% hydrolyzed, gives an 80% net yield of plastein from the synthesis reaction. However, these results ate based on a 1% protein solution used in the hydrolysis step this would be too low for an economical process (see Microbial transformations). 

Fluridone is a weak base with low water solubiUty. Sorption of fluridone increases with decreasing pH (436). Leaching of fluridone was not significant in field study, and the persistence has been determined to be less than 365 days. The degradation of fluridone appears to be microbial in nature, and accelerated breakdown of the herbicide occurs upon repeated appHcations (437). Fluorochloridone is shown to degrade by hydrolysis at pH 7 and 9, but not at lower pH. The half-Hves for this reaction are 190 and 140 days for pH 7 and 9, respectively. Breakdown by photolysis occurs rapidly with a half-hfe of 4.3 days at pH 7 (438). An HA is available for acifluorfen. 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

Once in the soil solution, urea—formaldehyde reaction products are converted to plant available nitrogen through either microbial decomposition or hydrolysis. Microbial decomposition is the primary mechanism. The carbon in the methylene urea polymers is the site of microbial activity. Environmental factors that affect soil microbial activity also affect the nitrogen availabiUty of UF products. These factors include soil temperature, moisture, pH, and aeration or oxygen availabiUty. 

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