Turnover of [14C]thiamin and activities of thiamin pyrophosphate-dependent enzymes in tissues of mice with Ehrlich ascites carcinoma.

Turnover of [14C]thiamin was studied in mice with Ehrlich ascites carcinoma fed a thiamin-deficient diet and injected with 5 or 2 micrograms/mouse of the labeled vitamin. The process of conversion of [14C]thiamin to thiamin pyrophosphate (TPP) was monitored by measuring the activities of transketolase, pyruvate dehydrogenase, and oxoglutarate dehydrogenase. The amount of coenzyme-unsaturated apotransketolase was assessed by measuring the TPP effect--determining transketolase activity with and without the addition of TPP in vitro. Tumor growth was accompanied by thiamin deficiency, manifested in an increase in [14C]thiamin incorporation into the host tissues and the absence of saturation of the tissues with the labeled vitamin over 13 days. Increased values for the turnover coefficients, reduction of thiamin-dependent enzyme activities, elevation of the TPP effect, and a decrease in urinary excretion of the radioactive products also provided evidence for a disturbance in thiamin metabolism. The severity of the disturbance in thiamin metabolism during malignant tumor growth was directly related to the dose of the exogenous vitamin.