Bacterial synthesis of thiamine

As in the synthesis of the thiazole nucleus, yeasts appear to utilize a quite different pathway from bacteria for the formation of the pyrimidine. While bacterial thiamin synthesis is inhibited by exogenous purines, thiamin production by yeast is unaffected. It... 

When considering sources of niacin, it should be noted that niacin can be, and is, synthesized by the intestinal flora. However, the amount produced is only of minor importance in the human. By contrast, as with thiamin and riboflavin, ruminants (cattle, sheep, etc.) have no dietary requirements for niacin because of bacterial synthesis in the rumen. 

Thus a thiamine derivative plays a metabolic role as cocarboxylase, which has been found to be inactivated by a specific phosphatase of yeast (122,123). The inactivation was inhibited by thiamine itself and to a lesser degree by thiamine monophosphate and the pyrimidine constituent of the thiamine molecule. Synthesis and breakdown of thiamine by Phycomyces species have also been studied (9,45,98). Pyridoxine derivatives are now known to catalyze two t3T)cs of bacterial reactions, involving transamination and decarboxylation of amino acids (4,32,35,59). Interconversion between members of the group of substances of natural occurrence which are related to pyridoxine has been observed in microorganisms and appears likely to afford a series of changes comparable to those observed in nicotinic acid dreivatives. Production of folic acid from chemically defined precursors by bacterial suspensions has also been observed (110,111). 

In 1914, Cooper (48) showed that alcoholic extracts of fowl s and rabbit s excreta possessed antineuritic potency. He postulated that although part of the vitamin content of the stools was derived from the unabsorbed residue, a substantial part was probably derived from bacterial synthesis. However, extracts of B, coli failed to exert a measurable antineuritic activity. Guerrant and Butcher (24, 25) later were able to show that the stools of rats on a B-deficient diet contained appreciable thiamin. The vitamin was apparently utilized by the screened animal, inasmuch as its requirement for the vitamin (26, 38) varied inversely with the extent of synthesis. The location of maximum synthesis (39) was found to be the large colon, particularly the cecum. It seemed probable that in cecec-tomized animals, part of the colon may assume the functim of the cecum (38, 40). 

Stereoselective carbon-carbon bond-forming reactions are among the most useful S5mthetic methods in asymmetric synthesis as they allow the simultaneous creation of up to two adjacent stereocenters. Acyloin formation mediated by thiamine diphosphate-dependent decarboxylase, yeast pyruvate decarboxylase, bacterial benzoylformate decarboxylase, and phenylpyruvate decarboxylase has been reported [142-147]. 

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