RESTORATION OF GLUCONEOGENESIS IN BIOTIN-DEFICIENT RATS

In our earlier study on gluconeogenesis in biotin-deficient rats we showed metabolic blocks at the pyruvate carboxylase and glyceraldehyde-3-P dehydrogenase steps. This resulted in an accumulation of pyruvate and lactate, and in a decrease in the level of malate and citrate in liver. The ratio of NADH NAD was also markedly reduced. The present study was made to ascertain how soon this condition is alleviated after biotin administration. Using 24-hr fasted biotin-deficient rats, the levels of pyruvate, lactate, malate, citrate, glucose, NADH and NAD were determined in rapidly frozen livers at 0, 1, 2, 4, and 8 hr after an injection of biotin. Incorporation of l-alanine-U-14C into blood glucose after biotin administration and the effect of actinomycin D and puromycin on this process was also studied. Within 2-4 hr after biotin administration, a marked increase in malate and citrate, and also in the reducing power, with a concomitant decrease in pyruvate was observed. The overall effect of the restoration of gluconeogenesis could be seen from the increased level of glucose in liver and blood and also from the increased incorporation of labeled alanine into blood glucose. Actinomycin D or puromycin administration prior to biotin injection failed to inhibit this restoration. The results indicate that there was no de novo synthesis of pyruvate apocarboxylase or the holocarboxylase synthetase and imply that (a) the lack of biotin was limiting holopyruvate carboxylase synthesis and (b) the decreased reducing power was limiting optimal glyceraldehyde-3-P dehydrogenase activity. © 1969.