Thiamine products

In a study of thiamin production by a strain of E. coli, Iwashima and Nose (70MI10400) noted that thiamin synthesis was repressed by addition of phenylalanine to the growth medium. The fact that this repression could be reversed by addition of the intact thiazole... 

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... 

Certain bacterial strains convert propylene glycol to pymvic acid in the presence of thiamine (15) other strains do the conversion without thiamine (16). Propylene oxide is the principal product of the reaction of propylene glycol over a cesium impregnated siHca gel at 360°C in the presence of methyl ethyl ketone and xylene (17). 

The sohd product and its aqueous solutions are mildly acidic and irritate the skin, eyes, and mucous membranes. The soHd material when moist generates the pungent, irritating odor of sulfur dioxide. Food-grade sodium metabisulfite is permitted ia those foods that are not recognized as sources of vitamin B, with which sulfur dioxide reacts (316) (see Vitamins,THIAMINE). 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

The thiol form (12) is susceptible to oxidation (see Fig. 2). Iodine treatment regenerates thiamine in good yield. Heating an aqueous solution at pH 8 in air gives rise to thiamine disulfide [67-16-3] (21), thiochrome (14), and other products (22). The disulfide is readily reduced to thiamine in vivo and is as biologically active. Other mixed disulfides, of interest as fat-soluble forms, are formed from thiamine, possibly via oxidative coupling to the thiol form (12). 

Worldwide production of thiamine was estimated at 3300 t in 1995. The principal suppHers were Hoffmann-La Roche, Takeda, and several Chinese factories. Prices in the United States were in the range of 20— 28/kg in 1995. 

A number of the genes involved in the biosynthesis of thiamine in E. coli (89—92), i hium meliloti (93), B. suhtilis (94), and Schi saccharomycespomhe (95,96) have been mapped, cloned, sequenced, and associated with biosynthetic functions. Thiamine biosynthesis is tightly controlled by feedback and repression mechanisms limiting overproduction (97,98). A cost-effective bioprocess for production of thiamine will require significant additional progress. 

Most of the thiamine sold worldwide is used for dietary supplements. Primary market areas include the following appHcations addition to feed formulations, eg, poultry, pigs, catde, and fish (see Feeds and feed additives) fortification of refined foods, eg, flours, rice, and cereal products and incorporation into multivitamins. Small amounts are used in medicine to treat deficiency diseases and other conditions, in agriculture as an additive to ferti1i2ers (qv), and in foods as flavorings. Generally for dry formulations, the less soluble, nonhygroscopic nitrate is preferred. Only the hydrochloride can be used for intravenous purposes. Coated thiamine is used where flavor is a factor. 

The pyruvate dehydrogenase complex (PDC) is a noncovalent assembly of three different enzymes operating in concert to catalyze successive steps in the conversion of pyruvate to acetyl-CoA. The active sites of ail three enzymes are not far removed from one another, and the product of the first enzyme is passed directly to the second enzyme and so on, without diffusion of substrates and products through the solution. The overall reaction (see A Deeper Look Reaction Mechanism of the Pyruvate Dehydrogenase Complex ) involves a total of five coenzymes thiamine pyrophosphate, coenzyme A, lipoic acid, NAD+, and FAD. 

O Nucleophilic addition of thiamin diphosphate (TPP) ylide to pyruvate gives an alcohol addition product. 

Step 4 of Figure 29.11 Elimination of Thiamin Diphosphate The product of the HETPP reaction with lipoamide is a hemithioacetal, which eliminates thiamin diphosphate vlide. This elimination is the reverse of the ketone addition in step 1 and generates acetyl dihydrolipoamide. 

Thiamine can be considered to be the product of the quatemization of 4-methyl-5-(2-hydroxymethyl)thiazole (5) by an active derivative of 4-amino-5-(hydroxymethyl)-2-methyl pyrimidine (4) (Scheme 2). In living cells, pyramine can be activated by conversion into the diphosphate 7, via monophosphate 6, and the substrate of the enzyme responsible for the quatemization is not the thiamine thiazole, but its phosphate 8. The product of the condensation, thiamine phosphate (9), is finally converted into diphosphate 2—the biochemically active derivative—by hydrolysis to free thiamine, followed by diphosphorylation, or more directly, in some cases. Enzymes are known for all of the steps depicted in Scheme 2, and adenosine triphosphate (ATP) is, as usual, the phosphate donor. 

The significance of these metabolites in the biosynthesis of the thiamine thiazole in considered next. Although, from their constitution, and from the tracer experiments, the metabolites are undoubtedly the products of transformation of 1-deoxy-D-t/ireo-pentulose, their significance in the biosynthesis of the thiazole of thiamine is not clear. The thiazole glycol is not a product arising from a transformation of the thiazole (5) of thiamine. Reduction to this thiazole (5) occurs in dialyzed extracts of disrupted cells, in the presence of ATP, NADH, and NADPH, but only at 0.2% the rate of synthesis of the thiamine thiazole (5) by intact cells. The behavior of the thiazole glycol on plates is merely a consequence of the extreme sensitivity of the tetrazolium reagent. 

Tetrahydrocannabinol (= THC)-11-carboxylic acid 290 Tetrahydrocortiso 221 Tetrahydrocortisone 221 Tetrahydrosteroids 222 Tetrazolium salts, reduction 61 Thalidomide 45 -, hydrolysis products 45 Thiabendazole 307, 308 Thiamine 235, 236, 397 Thickening agents 179 Thin-layer chromatography, advantage 5 -, numbers of publications per year 6 Thiobarbiturates 45,66 Thiocarbamide derivatives 322 Thiocarbamides, N -ary I-N -benzenesulfo-nyl- 248,249 Thiochrome 395... 

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

At the beginning of the MEP pathway, the glycolytic products, pyruvate and D-glyceraldehyde (GAP), are condensed in a transketolase reaction to deoxy-xylulose phosphate (DXP) by the deoxy-xylulose phosphate synthase (DXS) enzyme. DXP is the precursor for other pathways leading to pyridoxal and thiamine. 

---