Lysine synthesis

A wave of excitement was set in motion by this discovery. Soon afterwards it was demonstrated that poly (A) promotes poly lysine synthesis and poly(C) promotes polyproline synthesis. From these observations it seemed clear that the code words UUU, AAA, and CCC correspond to the amino acids phenylalanine, lysine, and proline, respectively. 

A similar reaction is catalyzed by homoaconitate hydratase (E.C. 4.2.1.36), which is an enzyme from the L-lysine synthesis that forms homocitric acid (2-hydrox-ybutane-l,2,4-tricarboxylic acid, 17) from homo-ris-aconitate (16)The enzyme 2-methylcitrate dehydratase (E. C. 4.2.1.79) catalyzes the addition of water to (Z)-but-2-ene-l,2,3-tricarboxylic acid (18) to yield 2-methylcitric acid (2-hydroxybutane-... 

These characteristics of lysine producers are combined to produce much stronger lysine producing strains. In addition to these fundamental properties, further addition of leucine requiring mutation is effective to increase the amount of lysine since in the mutant dihydrodipycolinate synthase is released from repression by leucine. The precursors of lysine synthesis include phosphoenol-pyruvate, pyruvate, and acetylCoA. In addition, many mutations are induced in the lysine producers to supply sufficient amounts of these precursors in good balance. These are deletion mutants of pyruvate kinase and show low activity of pyruvate dehydrogenase, etc. Furthermore, an alanine requirement was also reported to be effective in increasing the lysine amount. 

Aspartokinase is a major point of regulation of the biosynthetic pathways leading to threonine, lysine, and methionine. In bacteria, there are three isoenzymes of aspartokinase. Activity of one form is inhibited specifically by threonine and that of another form by lysine. Synthesis of the third form is inhibited by methionine. 

A further flux control step within L-lysine synthesis is the aspartate semialdehyde branch point. The aldehyde is either used as a substrate for the homoserine dehydrogenase, or together with pyruvate as a substrate for the dihydrodipicolinate synthase (Fig. 10). Whereas the homoserine dehydrogenase is allosterically controlled in its catalytic activity by the L-threonine concentration... 

Boustta, M., Huguet, J., and Vert, M., 1991, New functional polyamides derived from citric acid and L-lysine Synthesis and characterization, Makromol. Chem., Macromol. Symp., 47 345-355... 

In the case of dipicolinic acid, the biosynthetic pathway involves the formation of 2,3-dihydropicolinic acid which is an intermediate in lysine synthesis. See Pig. 2. (13)... 

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