Nitrogen enzymes

A class of enzymes found in bacteria within root nodules in some plants, which catalyze reactions by which N2 molecules from the air are converted to ammonia. For more information see Enzymes Nitrogen Cycle... 

Each step of the denitrification pathway is catalyzed by a distinct enzyme, nitrogen oxide reductase (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), that transfers electrons from the chain to the particular intermediate. Thermodynamically, in the absence of oxygen, nitrogen oxides are the most preferred electron acceptors by facultative bacterial groups. The role of nitrogen oxides in regulating organic matter decomposition has been discussed in earlier chapters (see Chapter 5). 

It is one of the wonders of life that simple bacteria can contain beautifully complex and vitally important enzymes such as nitrogenase. Because of this enzyme, nitrogen is continually cycled between its comparatively inert role in the atmosphere and its critical role in living organisms. Without nitrogenase, life as we know it could not exist on Earth. 

Nitrogen fixation a process in which atmospheric nitrogen is converted into ammonia. Activation of molecular nitrogen and its reduction to ammonia depend on the catalytic activity of the enzyme Nitrogen-ase (see). The ammonia is then incorporated into the various nitrogenous compounds of the cell by the processes of Ammonia assimilation (see). Nitrogenase is a very unstable enzyme, especially in anaerobic organisms. N.f. is fundament ly important for the ni-... 

The shape of a large protein is influenced by many factors including of course Its primary and secondary structure The disulfide bond shown m Figure 27 18 links Cys 138 of carboxypeptidase A to Cys 161 and contributes to the tertiary structure Car boxypeptidase A contains a Zn " ion which is essential to the catalytic activity of the enzyme and its presence influences the tertiary structure The Zn ion lies near the cen ter of the enzyme where it is coordinated to the imidazole nitrogens of two histidine residues (His 69 His 196) and to the carboxylate side chain of Glu 72... 

G. L. Coppoc and S. J. Leger, "Effect of Nitrogen Triduoride on Plasma Concentrations of Lactate, Methemoglobin, and Selected Enzymes," ApriWune 1968, SAM-TR-70-42 (AD 711044), School of Aerospace Medicine, Brooks Air Eorce Base, Texas, July 1970. 

Phospholipids. Phospholipids, components of every cell membrane, are active determinants of membrane permeabiUty. They are sources of energy, components of certain enzyme systems, and involved in Hpid transport in plasma. Because of their polar nature, phosphoUpids can act as emulsifying agents (42). The stmcture of most phosphoUpids resembles that of triglycerides except that one fatty acid radical has been replaced by a radical derived from phosphoric acid and a nitrogen base, eg, choline or serine. 

Animal metaboHsm is based on the reactions of oxygen and organic compounds containing carbon, hydrogen, oxygen, and nitrogen and other heteroatoms. Enzymes catalyze these biochemical oxidations, which are accompHshed at about 30—40°C and frequendy proceed stepwise to produce... 

Electrodes may also be rendered selective to more complex analytes using enzyme or other overcoats (see Biopolymers, analytical techniques Biosensors). The enzyme converts the analyte into a detectable ion or gas. Glucose and blood urea nitrogen sensors can be made in this way. 

The 4-piperazinyl nitrogen in pipemidic acid (69) has been alkylated, acylated and sulfonylated in the search for enhanced antibacterial activity, whilst the 3-pyrrolidinyl position in piromidic acid (68) is hydroxylated metabolically and enzymically to (74) (75MI21503), from which acyloxy derivatives have been prepared. 

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