Enzymes ammonia

Cell-free extracts of N. europaea will only oxidize hydroxylamine, probably because the enzyme responsible for the initial oxidation of ammonia is associated with the membrane and so is lost on disruption of the cell. This enzyme, ammonia monooxygenase, also catalyzes the oxidation of methane.1540 While the methane has a higher Km value for oxidation by ammonia monooxygenase than for oxidation by a methane monooxygenase, it is still possible that both processes would be catalyzed by ammonia monoxygenase in the natural environment. 

The first step in the nitrification process is the oxidation of ammonia to hydroxy-lamine by the enzyme ammonia monooxygenase (AMO) via the reaction ... 

Ammonia reacts with the ketone carbonyl group to give an mine (C=NH) which is then reduced to the amine function of the a ammo acid Both mine formation and reduc tion are enzyme catalyzed The reduced form of nicotinamide adenine diphosphonu cleotide (NADPH) is a coenzyme and acts as a reducing agent The step m which the mine is reduced is the one m which the chirality center is introduced and gives only L glutamic acid... 

Biosynthesis of Tea Flavonoids. The pathways for the de novo biosynthesis of flavonoids in both soft and woody plants (Pigs. 3 and 4) have been generally elucidated and reviewed in detail (32,51). The regulation and control of these pathways in tea and the nature of the enzymes involved in synthesis in tea have not been studied exhaustively. The key enzymes thought to be involved in the biosynthesis of tea flavonoids are 5-dehydroshikimate reductase (52), phenylalanine ammonia lyase (53), and those associated with the shikimate/arogenate pathway (52). At least 13 enzymes catalyze the formation of plant flavonoids (Table 4). 

Although the antibacterial and antifungal activities of bialaphos and phosphinothricin were not found to be usehil, the two agents were later used as biodegradeable, relatively nonselective, postemergent herbicides. Glutamine synthetase inhibition is toxic to plants because the enzyme is key to ammonia assimilation. There is some selectivity for individual plant species as shown by the LD for bialaphos ranging from 0.125 to 8.5 kg/ha (301—303). 

One of the most interesting uses for cinnamic acid in recent years has been as a raw material in the preparation of L-phenylalanine [63-91-2] the key intermediate for the synthetic dipeptide sweetener aspartame (25). Genex has described a biosynthetic route to L-phenylalanine which involves treatment of immobilized ceUs of R rubra containing the enzyme phenylalanine ammonia lyase (PAT,) with ammonium cinnamate [25459-05-6] (26). 

There are two distinct classes of enzymes that hydrolyze nitriles. Nittilases (EC 3.5.5. /) hydrolyze nittiles directiy to corresponding acids and ammonia without forming the amide. In fact, amides are not substrates for these enzymes. Nittiles also may be first hydrated by nittile hydratases to yield amides which are then converted to carboxyUc acid with amidases. This is a two-enzyme process, in which enantioselectivity is generally exhibited by the amidase, rather than the hydratase. 

Both threo- (14) and eo f >"4-fluoro-DL-glutamic acid (/5) are noncompetitive inhibitors of glutamine synthase, an enzyme that catalyzes the synthesis of glutamine from L-glutamic acid and ammonia. This mhibibon may explain the... 

The first step in the biological degradation of histidine is formation of a 4-methylideneimidazol-5-one (MIO) by cyclization of a segment of the peptide chain in the histidine ammonia lyase enzyme. Propose a mechanism. 

Reaction 1 is governed by the enzyme phenylalanine ammonia lyase. This enzyme normally conducts the breakdown of L-phenylalanine to from-cinnamic add and ammonia. However, die reaction can be reversed leading to the production of L-phenylalanine from frans-dnnamic add by using excess ammonia. 

Antineoplastic agents that cannot be grouped under subheadings 1-9 include miltefosine which is an alkylphosphocholine that is used to treat skin metastasis of breast cancer, and crispantase which breaks down asparagine to aspartic acid and ammonia. It is active against tumor cells that lack the enzyme asparaginase, such as acute lymphoblastic leukemia cells. Side effects include irritation of the skin in the case of miltefosine and anaphylactic reactions in the case of crispantase. Another recent development is the proteasome inhibitor bortezomib which is used to treat multiple myeloma. 

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