Biosynthesis of vitamin

In most bacteria, pyridoxal phosphate is synthesized by condensation between 4-hydroxythreonine and the pentose sugar 1-deoxy-xylulose phosphate, formed by condensation between pyruvate and glyceraldehyde 3-phosphate. The details of the pathway are not known. In plants, fungi, and some bacteria, the precursor is glutamine again, the pathway is unknown (Drewke and Leismer, 2001 Gupta et al., 2001). 

Decarboxylation aC—COOH Amino acid - primary amine -1- CO2 

Loss of side chain aC— 3C Threonine aldolase Serine hydroxymethyltransferase 

Elimination pc—R and aC—H Tryptophanase Serine dehydratase Aspartate p-decarboxylase 

Pyridoxal phosphate has a clear role in lipid metabolism as the coenzyme for the decarboxylation of phosphatidylserine, leading to the formation of phosphatidylethanolamine, and then phosphatidylcholine (Section 14.2.1), and membrane lipids from vitamin Bg-deficient animals are low in phosphatidylcholine (She et al., 1995). It also has a role, less well defined, in the metabolism of polyunsaturated fatty acids vitamin Bg deficiency results in reduced activity of A desaturase and impairs the synthesis of eicosapentanoic and docosahexanoic acids (Tsuge et al., 2000). 

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The study of the biosynthesis of vitamin B 2 is a saga whose resolution, due primarily to Battersby (80—83) and Scott (84,85), requited an effort on the same magnitude as the total synthesis. It was only when recent molecular biology tools became available to complement en2ymology, isotopic labeling, chemical synthesis, and spectroscopy that solution of this problem became possible. 

In 1973, the first naturally occurring isobacteriochlorin, iron-containing siroheme, was isolated1 from a sulfite reductase of Escherichia coli. Later it was also discovered in sulfite and nitrite reductases of numerous bacteria and plants.2 Iron-free sirohydrochlorins (also called factor II) were discovered in vitamin B12 producing bacteria.3-4 Together with factor III. a sirohydrochlorin methylated in the 20-position, the reduced forms of factor II and factor III were identified as biosynthetic intermediates in the biosynthesis of vitamin B12.5... 

Transformations of isobacteriochlorins are rare. The hydrogenation of isobacteriochlorins, e.g. 1,llb-24 ieacjs t0 dihydroisobacteriochlorins, e.g. 2. which are on the same oxidation level as hexahydroporphyrins or porphyrinogens. The dihydrogenated forms of sirohydrochlorin and 20-methylsirohydrochlorin (which are also called precorrin 2 and precorrin 3, respectively) have been identified as important intermediates in the biosynthesis of vitamin B, 2.5... 

Goodman, D. S. and H. S. Huang. 1965. Biosynthesis of vitamin A with rat intestinal enzymes. Science 149 879-880. 

In an inciteful discussion of insect-microbe relationships, Jones (10) postulated that insect-microbial associations, known to involve catabolic (e.g. cellulose-degrading) and anabolic (e.g. biosynthesis of vitamins, sterols, and amino acids) processes necessary to the survival of the host, could also include detoxification abilities. Most investigations in this area have been limited (11). Nevertheless, some studies indicate detoxification of terpenoids (12,... 

Interestingly, it is possible to isolate derivatives of vitamin Bj2 which lack the cobalt atom (65PNA(54)934, 70BBR(39)170>, and this has led to some speculation that insertion of cobalt may be one of the final steps in the biosynthesis of vitamin Bi2. 

UVB, between 290 and 330 nm, is the deeper region of biotic , that is biologically beneficial, UV radiation. Light of this wavelength region is used for the biosynthesis of vitamin D, and it produces pigmentation of the skin. 

In the biosynthesis of vitamin D substances, precursors include cholesterol (skin + ultraviolet radiation) in animals ergosterol (algae, yeast + ultraviolet radiation), Intermediates in the biosynthesis include preergocaldferol, tachysterol, and 7-dehydrocholesterol. Provitamins in very small quantities are generated in the leaves, seeds, and shoots of plants. In animals, the production site is the skin. Target tissues in animals are bone, intestine, kidney, and liver. Storage sites in animals are liver and skin. 

Several macrocyclic ligands are shown in Figure 2. The porphyrin and corrin ring systems are well known, the latter for the cobalt-containing vitamin Bi2 coenzymes. Of more recent interest are the hydroporphyrins. Siroheme (an isobacteriochlorin) is the prosthetic group of the sulfite and nitrite reductases which catalyze the six-electron reductions of sulfite and nitrite to H2S and NH3 respectively. The demetallated form of siroheme, sirohydrochlorin, is an intermediate in the biosynthesis of vitamin Bi2, and so links the porphyrin and corrin macrocycles. Factor 430 is a tetrahydroporphyrin, and as its nickel complex is the prosthetic group of methyl coenzyme M reductase. F430 shows structural similarities to both siroheme and corrin. 

The synthetic procedure involving ring contraction of hydroporphyrins has been applied only to the preparation of corrin complexes [78] and it has been inspired by the studies on the biosynthesis of Vitamin B12. The macroring precursor is the hexahydroporphyrin shown in Fig. 29. 

Biosynthesis of vitamin Bi2 and its analogs 91MI31 93AG(E)1223. Synthesis of biologically active a-tocopherol esters 91MI29. 

Early investigations of photosynthesis in bacteria and plants have led to a study of chlorins II. Quite recently the problem of biosynthesis of vitamin B12 has been shown to be connected to chlorins II, isobacteriochlorins III, and pyrrocorphins V. 

A particularly striking example of the importance of hydroporphyrins in nature is represented by the biosynthesis of vitamin B12 (85MI1). Some aspects of this metabolism outlined in Scheme 20 indicate that nearly the whole family of hydroporphyrins takes part in the reaction sequence either as intermediates or as equilibrating isomers. Biochemical problems in this field gave rise to many of the chemical activities described here. 

A hetero Diels-Alder reaction of a precursor 1-9 may be involved in the biosynthesis of the lignane carpanone 1-8 (Fig. 1-3), however, there is no proof for such an assumption [32]. On the other hand, it is well known that pericyclic reactions such as electrocyclic reactions and sigmatropic rearrangements occur in nature e.g. in the biosynthesis of vitamine D, vitamine B12 [33-35] and ecto-carpene [36]. 

Wolucka, B.A., and Van Montagu, M., 2003, GDP-Mannose 3, 5 -epimerase forms GDP-L-gulose, a putative intermediate for the de novo biosynthesis of vitamin C in plants. J. Biol. Chem. 278 47483-47490. 

BacherA, Eberhardt S, Fischer M,Kis K, and Richter G (2000) Biosynthesis of vitamin B2 [lihoiliLvin). Annual Reviews of Nutrition 20,153-67. 

Drewke C and Leistner E (2001) Biosynthesis of vitamin Be and structurally related... 

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