Lipoamide dehydrogenase in vitamin B2-deficient rat liver

The liver and the kidney of rats fed a B₂-deficient diet showed a decrease in lipoamide dehydrogenase (LADase) activity, 65% and 80% of those of rats fed on a B₂-supplemented diet, respectively, but the heart showed no decrease. The liver of B₂-deficient rats showed also a little decrease in the activity of glutathione reductase, while there were no differences in the activities of GOT and LDH in the liver between the B₂-deficient and B₂-supplemented rats. The activity of LADase in the cytosolic fraction of the liver, which was about one-tenth of that of mitochondrial fraction, was decreased in the B₂-deficient rats in a degree almost equal to the decrease in the activity in the mitochondrial fraction. The results obtained with single radial immunodiffusion test indicated that the decrease in the activity of LADase in B₂-deficient rats resulted from the decrease in the amount of the enzyme protein and that not only the livers of B₂-supplemented rats, but also of B₂-deficient rats contained no apoenzyme of LADase.