Thiamine, breakdown products

Using radio-labeled thiamine probes, a study of thiamine metabolism at normal loads produced an estimated half-life of thiamine of 9.5 to 18.5 days, and showed a large number of breakdown products in the urine. Several of these urinary catabolites are shown in Figure 30-9. 

As the proof for the structure of thiamine had depended so largely upon the synthesis of certain breakdown products, the complete synthesis of the vitamin was accomplished very soon afterwards. The first publication came from Williams and Clinei in the U.S. hard on their heels followed Todd and Bergelii jjj England and Andersag and Westphal in Germany. 

Figure 2. Formation of products from breakdown of cysteine and thiamine.

Thiamine labelled with or in the thiazole nucleus has been injected into rats i 22. The bulk of the radioactivity excreted in the urine was recovered as unchanged thiamine, but many other radioactive products were also discerned. Three of these were tentatively identified as thiochrome, thiamine disulfide and thiazole. In the experiments with sS, a considerable amount of radioactivity was recovered as sulfate. This indicates that a breakdown and oxidation of thiamine does take place, and there our knowledge ends for the moment. 

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). 

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