Content of tree and bound thiamine pyrophosphate (TPP) was measured by means of gel filtration and equilibrium dialysis procedures in mitochondria of normal rats, the rats under conditions of alimentary B1 avitaminosis and loading with thiamine. The content of protein-bound TPP was stable and equal to 20% of its total level in the mitochondria of control rats and in the rats loaded with thiamine. The content of free form of TPP was decreased in B1 avitaminosis; a severe form of the avitaminosis was accompanied by a decrease in content of the bound form. Concentration of the free form of TPP did not increase if the organism of the rats was loaded with thiamine. These data suggest existence of specific systems controlling the vitamin uptake in mitochondria. The active transport of thiamine across the mitochondrial membranes is considered as the most important process. Administration of the high doses of the vitamin led only to an increase in the non-coenzymatic form of the vitamin, indicating the absence of thiamine pyrophosphokinase in rat liver mitochondria. A possible mechanism of TPP transport in mitochondria is discussed.
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