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Catabolism in vitro of 2-¹⁴C-Thiazole-labeled Thiamine by Rat Tissues¹

Division of Nutrition, Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee

The catabolism in vitro of 2-¹⁴C-thiazole-labeled thiamine was studied by incubating it with rat liver homogenates. The criterion of thiamine breakdown was the production of ¹⁴CO₂. The results show that the rat tissues contain an enzyme system capable of causing the release of carbon dioxide from the 2 position of the thiazole moiety of thiamine. The amount of thiamine degraded in this manner is very small, however. Of the total amount of thiamine broken down, about 85% was degraded during the first 4 hours of incubation. Heating the homogenates for varying periods of time caused a considerable decrease in the activity of the enzyme. The amount of thiamine broken down by the liver of stock-fed rats was significantly greater (P < 0.01) than that from the thiamine-deficient or stock-fed animals fasted for 46 hours. The kidney was found to be 90% as active as liver; other tissues had much less activity. Several compounds including ethanol, methanol, thiazole (4-methyl-5-ß-hydroxyethyl thiazole), mercaptoethanol and folic acid were found to inhibit the enzyme activity. On an equivalent protein basis, mitochondrial and microsomal fractions had a greater enzyme activity than the nuclear and the supernatant fractions.

² Deceased.

Manuscript received 11 June 1969.