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Chapter 24 The biosynthesis of amino acids

Nitrogen is a key component of amino acids. Nitrogen gas is very unreactive molecule. Certain organisms such as bacteria that live in the root nodules of yellow clover can convert nitrogen gas into ammonia. Ammonia can then be used to synthesize first glutamate and then other amino acids.

24.0.1 An overview of amino acid synthesis
Ammonia is the source of nitrogen for the amino acid, the carbon backbone come from the glycolytic pathway, the pentose phosphate pathway, or the citric acid cycle. The stereochemistry at the α-carbon atom is established by a transamination reaction that involves pyridoxal phosphate. Aminotransferase proteins have a common fold.

24.1 Nitrogen fixation: microorganisms use ATP and a powerful reductant to reduce atmospheric nitrogen to ammonia Symbiotic Rhizobium bacteria invade the roots of leguminous plants and form root nodules in which they fix nitrogen.

Nitrogen fixation by nitrogenase complex. Electrons flow from ferredoxin to the reductase to nitrogenase to reduce nitrogen.

24.1.1 The iron-molybdenum cofactor of nitrogenase binds and reduces atmospheric nitrogen
Both reductase and nitrogenase are iron-sulfur proteins, in which iron is bonded to the sulfur atom of a cysteine residue and to inorganic sulfide.

Fe protein. This protein is a dimer composed of two polypeptide chains linked by a Fe-4S cluster. Each monomer is a member of the P-loop NTPase family and contains an ATP-binding site.

MoFe protein. This protein is an heterotetramer composed of two αsubunits and two βsubunits. It contains two copies each of two types of clusters: P clusters and FeMo cofactors. P cluster contains 8 irons and 7 sulfides linked to 6 cysteines. MoFe contains 1 molybdenum,7 irons, 9 sulfides, 1 homocitrate is linked to 1 cysteine and 1 histidine.

Nitrogen-reduction site. The FeMo cofactor contains an open center that is the likely site of nitrogen binding. The formation of...

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