Thiamine pyruvate with carboxylase

Indeed both -lactylthiamine pyrophosphate (XX) and a-hydroxyethyl-thiamine pyrophosphate (XXI) have been isolated and identified as products after incubation of pyruvate with a purified carboxylase preparation " . When [2- - C]pyruvate is used, the radioactivity is found in the thiazole part of the molecule after sulfite cleavage of XXL Acetaldehyde is formed from pyruvic acid by yeast carboxylase by enzymic cleavage of intermediate XXI, Uberating thiamine pyTophosphate . XXI has also been identified as intermediate in the formation of acetyl-coenzyme A from pyruvic acid by p3u uvic oxidase . The transketolase reaction has been shown to proceed via a gly-colaldehyde-enzyme intermediate here one may expect to find dihydroxy-ethylthiamine pyrophosphate as active glycol-aldehyde . Such experiments strongly support Breslow s concept of the reaction mechanism. 

The answer is B. While all of the listed conditions are consistent with lethargy and developmental defects, the lactic acidosis rules out pyruvate kinase deficiency. Thiamine and niacin deficiencies are unlikely due to the lack of effect of vitamin supplementation. Excess pyruvate is the source of the elevated alanine in the serum. The clinical findings are thus consistent with pyruvate carboxylase deficiency, which is associated with severe hypoglycemia due to fasting due to impaired gluconeogenesis. 

Mizuhara [65] developed a more adequate model by demonstrating that thiamine catalyzes the decarboxylation of pyruvic acid in basic aqueous solution (pH 8.8). Acetoin is the final product of the reaction. Breslow [66] later showed that the hydrogen in position 2 of the thiazole ring of the coenzyme is exchanged with deuterium when deuterium oxide (D2O) is added to the incubation system. Thus, carbon 2 of the thiamine appears to react in this chemical process. The hydrogen in position 2 is acidic and is thus readily ionized to an anion in basic media (see Fig. 4-7). On the basis of these findings, researchers have proposed the following sequence of reactions to explain the catalytic action of carboxylase. The carbon 2 of the thiazo-... 

Magnesium is closely associated with calciiun and phosphorus. About 70 per cent of the total magnesium is found in the skeleton but the remainder, which is distributed in the soft tissues and fluids, is of crucial importance to the well-being of the animal. Magnesium is the commonest enzyme activator, for example in systems with thiamin pyrophosphate as a cofactor, and oxidative phosphorylation is reduced in magnesium deficiency. Magnesium is an essential activator of phosphate transferases (e.g. creatine kinase) and it activates pyruvate carboxylase, pyruvate oxidase and reactions of the tricarboxylic acid cycle therefore, it is essential for the... 

The structure of cocarboxylase (see Fig. 1 for formula) was established by Lohmann and Schuster. A long-established function of cocarboxylase (thiamine pyrophosphate, aneurin) is as the coenzyme of a-ketoaeid carboxylase. Mg++ is also required. The reaction involved is the nonoxidative decarboxylation of an a-keto acid to CO2 and an aldehyde with one less carbon atom. The most important example is the splitting of pyruvic acid to acetaldehyde and CO2 (equation 9). This... 

The coenzyme of carboxylase (thiamine pyrophosphate) was shown to be the active form of vitamin B, a method for its estimation was developed, its enzymatic synthesis in animal tissues was demonstrated. Perhaps the most important part of Ochoa s work at Oxford was the discovery of the coupling of phosphorylation with oxidation of pyruvic acid in brain. Here he demonstrated the obligatory relationship between these two processes, a contribution which came almost at the same time as the observations of Herman Kalckar in Denmark and Vladimir A. Belitzer in the Soviet Union. Ochoa was the first to show the formation of three phosphate bonds for each oxygen atom used in the process. 

At autopsy, multiple areas of necrosis are found in the grey matter of the central part of the brain and in the spinal cord [141]. Leigh compared these changes to Wernicke s encephalopathy, though with a different distribution. This suggested either thiamine deficiency or inability to utilize thiamine normally, but treatment with thiamine or thiamine pyrophosphate has no effect on the course of the disease [142]. Lipoic acid, like thiamine pyrophosphate involved in the oxidative decarboxylation of pyruvic acid, has been given to some patients [137] the concentration of pyruvic acid in the blood fell and clinical improvement was claimed. Others have tried lipoic acid treatment with less success—the pyruvic acid content of the blood fell, but there was no effect on the clinical course of the disease [136]. It is now known that the enzymes dec2irboxylating pyruvic acid are normal and that the metabolic error results from a lack of pyruvate carboxylase. 

Brunette, M.G., Delvin, E., Hazel, B. and Scriver, C.R. (1972), Thiamin responsive lactic acidosis in a patient with deficient low Km pyruvate carboxylase activity in liver. Pediatrics, 50,702. 

Maesaka, H., Kamiya, K., Misugi, K. and Tada, K. (1976), Hyperalaninemia, hyper-pyruvicemia, and lactic acidosis due to pyruvate carboxylase deficiency of liver. Treatment with thiamine and lipoic acid. Eur. J. Pediatr., 122,159. 

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