Thiamine pyrophosphate effect

Puxty JA, Haskew AE, Ratcliffe JG, McMurray J. Changes in erythrocyte transketolase activity and the thiamine pyrophosphate effect during storage of blood. Ann Clin Biochem 1985 22 (Pt 4) 423-7. 

Vitamin deficiency of Bj leads to the disease known as Beriberi. However, nowadays in the Western hemisphere, vitamin Bj deficiency is mainly found as a consequence of extreme alcoholism. In fact, the vitamin absorption by the gut is decreased and its excretion is increased by alcohol. Alcohol also inhibits the activation of vitamin Bj to its coenzyme form, thiamine pyrophosphate ester (TPP). There is no evidence of adverse effects of oral intake of thiamine [417]. The main food sources of vitamin Bj are lean pork, legumes, and cereal grains (germ fraction). It is soluble in water and stable at higher temperature and at pH lower than 5.0, but it is destroyed rapidly by boiling at pH 7.0 or above. 

Effective concentration 65-72 entropy and 68-72 in general-acid-base catalysis 66 in nucleophilic catalysis 66 Elastase 26-30, 40 acylenzyme 27, 40 binding energies of subsites 356, 357 binding site 26-30 kinetic constants for peptide hydrolysis 357 specificity 27 Electrophiles 276 Electrophilic catalysis 61 metal ions 74-77 pyridoxal phosphate 79-82 Schiff bases 77-82 thiamine pyrophosphate 82-84 Electrostatic catalysis 61, 73, 74,498 Electrostatic effects on enzyme-substrate association rates 159-161... 

A macrobicyclic thiazolium cyclophane 84 functions as a model of thiamine pyrophosphate-dependent ligases and effects benzoin condensations [5.38, 5.65a, A.l 1], Acyl transfer is catalysed by formation of a ternary complex between a cyclophane receptor and two substrates [5.65b]. 

The ALS isolated as described in Table III displayed typical Michaelis-Menten kinetics with respect to pyruvate with a Km of 2.44 mM. Substrate concentrations as high as 50x Km had no effect on the rate of the reaction. Thiamine pyrophosphate, FAD and Mg(2+) were an absolute requirement for catalysis by the purified enzyme. These properties are consistent with observations made by others (30). Optimum activity was obtained at pH 7.1 and 37C, which were also the best conditions for inhibition by TP. There was no significant difference in the 1(50) value of TP whether ALS was taken after step 2 or 5, indicating low potential for non-specific binding of the herbicide to other proteins. 

Vitamin Bj Vitamin Bj was discovered in 1926 by Jansen and Do-NATH, who synthesized it in its crystalline form from rice bran. It was initially called aneurine due to its antipolyneuropathic effect. Because it contains sulphur, Windaus correctly renamed it thiamine in 1932, a term by which it is still known today. The stixicture of this vitamin was described by Williams and Grewe in 1936. It is made up of pyrimidine and thiazole. Thiamine occurs in nature as free thiamine and in the form of thiamine monophosphate, diphosphate and triphosphate. A maximum amount of 8 — 15 mg is absorbed daily in the proximal portion of the small intestine. In the case of oversupply, thiamine is neither stored nor intestinally absorbed. A regular intake, with a daily requirement of about 1 mg, is necessary. The major coenzyme is thiamine pyrophosphate (TPP). Thiamine deficiency may be caused by malnutrition, impaired absorption, alcoholism, antithiamines or a lack of magnesium. Magnesium is an important cofactor for the coenzyme thiamine pyrophosphate. 

Pyruvate oxidase requires the presence of thiamine pyrophosphate (0.1 mmol/1) and Ca2+ (2.5 mmol/1) for maximum activity. It should be used in 40 mmol/1 Tris buffer, pH 6.5-7.5, containing 0.5 mmol/1 phosphate. At higher phosphate concentrations substrate inhibition occurs this effect has been utilized in a phosphate sensor based on immobilized PyOD (Tabata and Murachi, 1983). Since PyOD is relatively unstable, for biosensors the enzyme has been immobilized by physical entrapment in, e.g., collagen (Mizutani et al., 1980), poly(vinyl chloride) and acetylcellulose (Kihara et al., 1984a,b). 

Pyravate synthase is distinct from pymvate dehydrogenase, for which the isotope effect at C-3 is ca. 9%o (Melzer and Schmidt 1987). Both enzymes use thiamine pyrophosphate as a cofactor. 10. PreuB et al. 

At present, the important clinical indication areas for therapy with thiamine are the beriberi of alcoholics and Wernicke s encephalopathy (Korner and Vollm 1976). In both cases, therapy is started with daily doses of at least 50-100 mg (in severe cases up to 200 mg) thiamine administered parenterally. Therapy is then continued with oral doses of 100-300 mg daily. Neuritis accompanying pregnancy responds particularly well to vitamin therapy. In some severe disorders of the intermediate metabolism (e.g., diabetic acidosis, severe hepatic malfunction), the necessary phosphorylation of thiamine in the organism is no longer ensured. Thiamine has, therefore, to be administered directly in its active form, thiamine pyrophosphate (TPP, cocarboxylase). Instances of toxicity of thiamine have been reported, primarily showing effects on the cardiovascular and nervous systems (Un-NA 1972 DiPalma and Ritchie 1977). 

Kuriyama, M., Yokomine, R., Arima, H., Hamada, R., and Igata, A., 1980. Blood vitamin Bl, transketolase and thiamine pyrophosphate (TPP) effect in beriberi patients, with studies employing discriminant analysis. Clinica Chimica Acta. 108 159-168. 

According to Breslow, the active aldehyde intermediate in the decarboxylation of pyruvate could be an a-hydroxyethyl derivative of thiamine pyrophosphate, the substituent being attached in position 2 to the thiazole ring . His starting point was the observation that thiazolium salts easily lose a proton at C-2. Thus a stable and reactive zwitterion results that could be capable of forming an acyl carbanion derivative. The near-by amino-pyrimidine ring would have an inductive effect upon electron withdrawal at C-2. Breslow pictures the formation of acetoin from pyruvate and acetaldehyde as follows ... 

F. Jordan and Y. H. Mariam (1978), V -Methylthiaminium diiodide. Model study on the effect of a coenzyme bound positive charge on reaction mechanism requiring thiamine pyrophosphate. J. Amer. Chem. Soc. 100, 2534-2541. 

However both can be cleaved by alkali to form UMP and the phosphate derivative of the carbohydrate. The pyrophosphate bond may also be split by a nucleotide pyrophosphatase from potatoes (338) or kidney (339). The enzyme is effective on DPN, DPNH, TPN, ADP, ATP, thiamine pyrophosphate, and FAD. 

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