Enzyme systems decomposition

Biological Decay. The two major enzyme systems that are used to control intracellular H202 concentrations in organisms are catalases and peroxidases (47). The different overall reactions for H202 decomposition mediated by these two enzyme systems can be illustrated as follows for catalase ... 

The two major enzyme systems that lead to the decomposition of H202 are catalases and the peroxidases. By using 1802, Moffett and Zafiriou (1) showed that catalase is responsible for 65-80% of the decomposition of H202 and that peroxidase-mediated decay accounts for 20-35% of the loss. These experiments have not been extended to freshwater systems, and therefore the relative contribution of the two enzyme systems has not been established. 

In the following discussion, we have assumed that wood decay is due to the concerted action of the individual enzyme systems responsible for cellulose, hemicellulose, and lignin decomposition. 

Furukawa, N. and K. Tonomura. 1971. Enzyme system involved in the decomposition of phenyl mercuric acetate by mercury-resistant Pseudomonas. Agric. Biol. Chem. 35 604-610. 

Preparations containing parathion are turned brown by the action of strong sunshine and are decomposed. This may explain why parathion is rather rapidly deactivated on green plant surfaces. Its action on living plants lasts 1-8 days, which is a fraction of the duration of action measured on lifeless surfaces, an obvious indication that the rapid decomposition is caused for a great part by the enzyme system of the plant. 

The final decomposition products of dealkylated and/or dealkoxylated urea herbicides, the respective anilines are not stable but are further transformed by the enzyme systems of the plants by oxidation or conjugation (Onley et al., 1968). 

One of the most used systems involves use of horseradish peroxidase, a 3-diketone (mosl commonly 2,4-pentandione), and hydrogen peroxide." " " Since these enzymes contain iron(II), initiation may involve decomposition of hydrogen peroxide by a redox reaction with formation of hydroxy radicals. However, the proposed initiation mechanism- involves a catalytic cycle with enzyme activation by hydrogen peroxide and oxidation of the [3-diketone to give a species which initiates polymerization. Some influence of the enzyme on tacticity and molecular... 

Analysis of reaction mixtures for 1-propanol and 2-propanol following incubation of NDPA with various rat liver fractions in the presence of an NADPH-generating system is shown in Table I ( ). Presence of microsomes leads to production of both alcohols, but there was no propanol formed with either the soluble enzyme fraction or with microsomes incubated with SKF-525A (an inhibitor of cytochrome P450-dependent oxidations). The combined yield of propanols from 280 ymoles of NDPA was 6.1 ymoles and 28.5 ymoles for the microsomal pellet and the 9000 g supernatant respectively. The difference in the ratio of 1- to 2-propanol in the two rat liver fractions may be due to differences in the chemical composition of the reaction mixtures (2) Subsequent experiments have shown that these ratios are quite reproducible. For comparison, Table I also shows formation of propanols following base catalyzed decomposition of N-propyl-N-nitrosourea. As expected (10,11), both propanol isomers were formed, the total yield in this case being almost quantitative. 

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