The determination of thiamin pyrophosphate in blood and other tissues, and its correlation with erythrocyte transketolase activity.

A sensitive method for the specific measurement of thiamin pyrophosphate (TPP) has been developed using the apoenzyme recombination concept. Yeast pyruvic decarboxylase apoenzyme can be reconstituted by the addition of TPP or samples containing TPP, yielding the holoenzyme with activity proportionate to the amount of TPP added. Using this technique, reaction mixtures containing 0.2 to 1.5 ng TPP can be assayed. Normal human erythrocyte TPP ranges from 50 to 150 ng per ml packed cells. When rats are fed a thiamin deficient diet, the erythrocyte TPP level falls more rapidly than the erythrocyte transketolase activity. After 8 days, the level of TPP in the erythrocytes of deficient animals was 10% of the level in pair-fed controls. At this time, however, there was no appreciable decrease in their respective transketolase activities. The level of TPP in the liver also is decreased drastically after 8 days. Therefore it appears that erytyrocyte and liver TPP stores have begun to be depleted and suggest that erythrocyte TPP levels are a more sensitive indicator of thiamin status.