4- Phosphohydroxy-L-threonine

Pyridoxol (vitamin Bg). Again 1-deoxyxylulose 5-P serves as a precursor.378 In E. coli only two genes have been implicated in the condensation of this compound with 4-(phosphohydroxy)-L-threonine (Fig. 25-21, step/) 378a One is an NAD+-dependent dehydrogenase that acts on the second substrate prior to the condensation. Significant differences from the path-... 

P serves as a precursor. In E. coli only two genes have been implicated in the condensation of this compound with 4-(phosphohydroxy)-L-threonine (Fig. 

Two pathways for PLP biosynthesis de novo are known in plant and microorganisms. The first was extensively studied in Escherichia coli. This pathway is articulated in two branches which join in a ring closure reaction catalysed by PNP synthase. One branch started from pyruvate and glycer-aldehyde 3-phosphate and the other from 4-phosphohydroxy-L-threonine (derived from erythrose 4-phosphate). The second route is when PLP is formed from glutamine, either ribose 5-phosphate or ribulose 5-phosphate and either dihydroxyacetone phosphate or glyceraldehyde 3-phosphate by action of the PLP synthase complex (Roje 2007). This pathway was discovered in fungi and it has become clear that it is much more widely distributed than the first pathway. It exists in Archaea, most eubacteria and plants. 

Prokaryotic organisms synthesise a primary form of vitamin pyridoxol 5 -phosphate from 1-deoxy-D-xylulose 5-phosphate (l-deoxy-D-t/treo-pent-2-ulose 5-phosphate) and 2-amino-2-deoxy-D-threo-tetronic (2-amino-2-deoxy-D-threonic) acid, known as 4-(phosphohydroxy)-L-threonine or 4-hydroxy-i-threonine 4-phosphate. Phosphohydroxythreonine arises from D-erythrose 4-phosphate, a product of decomposition of D-fructose 6-phosphate. Non-phosphorylated forms (pyridoxal, pyridoxol and pyridoxamine) are produced by hydrolysis of the corresponding phosphates. Animals do not synthesise vitamin Bg de novo, only convert the non-phosphorylated forms in the Hver, erythrocytes, and other tissues into the corresponding phosphates and the individual forms of each other. Pyridoxal 5 -phosphate arises by oxidation of pyridoxol 5Lphosphate and transamination of pyridoxal 5 -phosphate provides pyridoxamine 5Lphosphate. Both these forms of vitamin Bg are catalytically active. Pyridoxal 5 -phosphate... 

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See also in sourсe #XX -- [ ]

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